A measure or set of measures designed to perma­nently eliminate a hazard

Absolute humidity

Air’s moisture content expressed in grains or pounds of water vapor per pound of dry air.


The ratio of a solar energy absorbed to incident solar. Also called absorbtivity.


A solid material’s ability to draw in and hold liquid, gas, or radiant energy.

Accent Lighting

Accent lighting illuminates walls, reduces brightness and contrast between walls and ceilings or windows.

Acoustical Sealant

Sealing agent used to minimize the entry or exit of sound from an interior space.


The number of times in one hour that all of the air in a home is replaced by outside air through air leakage and/or ven­tilation.


Adhesion of a thin layer of molecules to a surface they contact.

Air Barrier

Any part of the building shell that offers resistance to air leakage. The air barrier is effective if it stops most air leak­age. The primary air barrier is the most effective of a series of air barriers.

Air Changes per Hour at 50 Pascals (ACH50)

The number of times the volume of air in a structure will change in one hour at the induced blower door house pressure of 50 pascals.

Air Changes per Hour Natural (ACHnat)

The number of times the indoor air is exchanged with the outdoor air in one hour under natural driving forces. It can be estimated using a blower door.

Air conditioning

Cooling buildings with a refrigeration system. More generally means both heating and cooling.

Air Conditioning Contractors of America (ACCA)

Industry group that works toward improving the air conditioning indus­try, promoting good practices and keeping homes and buildings safe, clean, and comfortable.

Air exchange

The process whereby indoor air is replaced with the outdoor air through air leakage and ventilation.

Air-free carbon monoxide

A measurement of CO in an air sam­ple or flue gas that takes into account the amount of excess air (oxygen, O2) in the sample, incorporating an adjustment to the as-measured CO ppm value, thus simulating air-free (oxygen-free) conditions in the sample. Usually measured in units of parts per million (ppm).

Air handler

A steel cabinet containing a blower with cooling and/or heating equipment and connected to ducts that transport indoor air to and from the air handler.

Air-handling unit (AHU)

See air handler.

Air leakage

Uncontrolled ventilation through gaps in the pres­sure boundary. Typical sites of air leakage include around win­dows, pipes, wires and other penetrations.

Air-impermeable insulation

An insulation having an air perma­nence equal to or less than 0.02 L/s-m2 at 75 Pa pressure differ­ential tested according to ASTM E 2178 or E 283.

Air sealing

Air sealing is a systematic approach to reducing air leakage in a building.


The ratio of reflected to incident light.

Altitude adjustment

The input modification for a gas appliance installed at a high altitude. When a gas appliance is installed more than 2000 feet above sea level, its input rating may be reduced by approximately 4 percent per 1000 feet above sea level.


Of the surrounding area or environment.

Ambient air

Air in the habitable space. Also the air around a human observer.

Ambient lighting

Lighting spread throughout the lighted space for safety, security, and aesthetics.

American Gas Association (AGA)

A trade association represent­ing American natural gas supply companies. AGA collaborates with ASC and NFPA on the National Fuel Gas Code.

American National Standards Institute, Inc. (ANSI)

A private non-profit organization that oversees the development of volun­tary consensus standards for products, services, processes, sys­tems, and personnel in the United States.

American Recovery and Reinvestment Act (ARRA)

Bill signed by President Obama in February 2009 as an economic stimulus package

American Society of Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE)

A technical society for individuals and organizations interested in heating, ventilation, air-condition­ing, and refrigeration. ASHRAE publishes standards and guide­lines relating to HVAC systems and issues.

American Society for Testing and Materials (ASTM)

A stan­dards organization that develops and publishes voluntary con­sensus technical standards for a wide range of materials, products, systems, and services.


The rate that electrical current flows through an appliance at any given time; also called current.


A unit that measures the rate that electrons move through a conductor. It is comparable to a measurement of water flow.


A device for measuring air speed, used in weath­erization work to determine flow rates at registers.

Annual Fuel Utilization Efficiency (AFUE)

A laboratory-derived efficiency for heating appliances that accounts for chimney losses, jacket losses, and cycling losses, but not distribution losses or fan/pump energy.

Annual return

The annual savings divided by the initial cost of an ECM, expressed as a percent.


Any device powered by electricity or combustion fuel.

Approach temperature

The temperature difference between the fluid inside a heat exchanger and the fluid outside it.


A heating control device that controls the burner or the circulator in a hydronic heating system


Length x width = area

As-measured Carbon Monoxide

A calculation of CO in parts per million (ppm) of a combustion-gas sample with the excess air (oxygen, O2), diluting the CO concentration removed by the calculator in the fuel-gas analyzer.


American Society of Heating, Refrigerating, and Air-Conditioning Engineers. International technical society which develops standards for those concerned with refrigeration pro­cesses and the design and maintenance of indoor environments.

ASHRAE 62.2-20xx

Air quality standard developed for low-rise residential buildings. Defines the roles of an minimum require­ments for mechanical and natural ventilation systems and the building envelope. The most current standard of time of writing was ASHRAE 62.2-2013.


A fibrous mineral with fireproofing and insulating characteristics manufactured into a variety of building materi­als. Small, sharp, asbestos fibers are a known carcinogen when inhaled.

Association of Energy Engineers (AEE)

A professional organiza­tion for energy engineers. AEE offers many certification pro­grams, including one for residential energy auditors.

Association of Home Appliance Manufacturers (AHAM)

Trade association representing the appliance manufacturing industry

Atmospheric appliance

A combustion appliance that burns and exhausts its combustion gases at atmospheric pressure.

Atmospheric pressure

The weight of air and its contained water vapor on the surface of the earth. At sea level this pressure is 14.7 pounds per square inch.


The unfinished space between the ceiling assembly of the top story and the roof assembly.

Attic, habitable

A finished or unfinished area, not considered a story. See the IRC for specific requirements.


The process of identifying energy conservation opportu­nities in buildings.

Auxiliary heat

Electric resistance heat in a heat pump that heats the building when the compressor isn’t able to provide the entire heat capacity needed for cold weather.

Awning window

Awning windows are essentially casement win­dows that swing vertically. Awning windows are often used in basements. Jalousie windows, found on older mobile homes, are a type of awning window.


A double-wall pipe for gas- or propane-fired combus­tion appliances.


Continuous spillage of combustion gases from a vented combustion appliance into the conditioned space.

Backdraft damper

A damper, installed near a fan, that allows air to flow in only one direction.

Backer rod

Polyethylene foam rope used as a backer for caulk­ing.


1. A lightweight plate that directs air from a soffit over attic insulation and along the bottom of the roof deck to venti­late the attic and cool the roof deck. 2. A plate or strip designed to retard or redirect the flow of flue gases.

Balance point

The outdoor temperature at which no heating is needed to maintain inside temperatures.


A coil of wire or electronic device that provides a high starting voltage for a lamp and limits the current flowing through it

Balloon framing

A method of construction in which the vertical framing members (studs) are continuous pieces running the entire height of the wall.

Band joist

See - Rim Joist

Barometric Vent Damper

A device installed in the heating unit vent system to control draft. Usually used on oil-fueled units or gas units with power burners


Material used to block passage or movement.


That portion of a building that is partly or completely below grade.


A blanket of preformed insulation, generally 14 inches to 23 inches wide, and varying in thickness from 3.5 inches to 10 inches.


A strong horizontal building support used to carry the weight of a floor or roof.

Belly blow

A process for re-insulating floor cavities with blown-in insulation.

Belly return

A configuration found in some mobile homes that uses the belly cavity as the return side of the heating/cooling dis­tribution system.

Bimetal element

A metal spring, lever, or disc made of two dis­similar metals that expand and contract at different rates as the temperature around them changes. This movement operates a switch in the control circuit of a heating or cooling device.


A construction element or material used to prevent the movement of air or insulation into or through building cavi­ties.

Block Frame

A non-finned frame that can be used as new or retrofit installation in a block wall application or as a wood win­dow replacement frame.

Blower Door

A blower door is a diagnostic tool used to locate the points of infiltration in the building envelope and help pri­oritize the air sealing protocols.


The act of removing water from a boiler to remove sediment and suspended particles.

Blower Fan

The squirrel-cage fan in a furnace or air handler.

Blown Insulation

A loose-fill insulation that is blown into attics and building cavities using an insulation blowing machine.

Board Feet

A measurement of lumber volume. A board foot equals 144 cubic inches of wood


A fossil fuel appliance used for producing hot water or steam as the medium to distribute heat to the dwelling unit.


A duct section that connects between a duct and a register or between round and square ducts

Bonus Room

A room that does not meet building code require­ments in order to be habitable.


An inspection tool; a reflexible tube with a light and camera or viewer at one end. Boroscopes can be used to look into wall cavities and other tight spaces that would be otherwise impossible to visually inspect.


Defines where an area ends and another begins.

Branch Circuit

An electrical circuit used to power outlets and lights within a home.

Branch Duct

An air duct which branches from a main duct.


The intensity of the sensation derived from viewing a lit surface. Measured in footlamberts, it is also called luminance or luminous intensity.

British Thermal Unit (Btu)

The quantity of heat required to raise the temperature of one pound of water one degree Fahren­heit.


British Thermal Units per hour.

Building Cavities

The spaces inside walls, floors, and ceilings between the interior and exterior sheeting

Building Envelope

The area of the building that encloses its con­ditioned and unconditioned spaces.

Building Management System (BMS)

Computer-based control system installed in buildings that controls and monitors the building's mechanical and electrical equipment such as air han­dling and cooling.

Building Performance Institute (BPI)

Organization supporting the development of a highly professional building performance industry through individual and organizational credentialing and a quality assurance program.

Building Science

A complex perspective on buildings, using contemporary technology to analyze and solve problems of design, construction, maintenance, safety, and energy efficiency.

Building Shell

Separates a building’s indoors from the outdoors.

Building Tightness Limit (BTL)

Calculation procedure, expressed in units of CFM50, based on the American Society of Heating, Refrigerating and Air- Conditioning Engineers Stan­dard 62-2001, Ventilation for Acceptable Indoor Air

Bulk Moisture

Large amounts of water intrusion, for example from wind-driven rain or sub-surface water.


A device that facilitates the burning of a fossil fuel, like gas or oil.

Butyl-backed tape

Heavy-duty, pressure-sensitive duct joint rolled sealant.


An air leakage site that allows air to leak out of a build­ing passing around the air barrier and insulation.

Cad Cell

A flame sensor composed of the chemical compound cadmium sulfide. Its purpose is to sense whether a flame is pres­ent during a burner cycle. If a flame is not detected, it activates a relay, which shuts the burner down.


Comparison of the test results of an instrument to a known reference point.


Having a weatherization team return to a job site to perform work not done or redo work done unsatisfactorily.

Can light

A light fixture (or can) that is set into the ceiling. Also called a recessed light fixture.


A projecting structure, such as a beam, that is sup­ported at one end and carries a load at the other end or along its length.

Cantilevered Floor

A floor that extends beyond the foundation of the framed structure below it.

Cape Cod

A house design featuring a finished attic space, also called a one-and-a-half story.

Capillary action

The ability of water to move through materials, even upward against gravity, through small tubes or spaces.

Capillary barrier

A material or air space designed to stop capil­lary action from carrying water into a building.

Carbon Dioxide (CO2)

A heavy, colorless, nonflammable gas formed by the oxidation of carbon, by combustion, and by the respiration of plants and animals. One of two main products of complete combustion of a hydrocarbon (the other is water vapor).

Carbon Monoxide (CO)

Carbon Monoxide is a tasteless, odor­less, colorless and poisonous gas that is a by-product of incom­plete combustion of fossil fuels. It is usually caused by a lack of air to support combustion or impingement of the flame.

Casement Window

Casement windows have a single operable sash that swings outward on a horizontal plane. Casement win­dow frames that have gone out of square due to settling can stick and quite possible render these types of windows inoperable.


Exposed molding or trim around a window or door.

Cathedral Ceiling

A pointed or slanting celling of a room that rises through more than one floor.

Cathedralized Attic

An attic that is insulated at the underside of the roof deck rather than at the ceiling.


Mastic compound for filling joints and cracks.


 A temperature scale on which water freezes at 0°C and boils at 100°C.

Cellulose Insulation

Insulation, packaged in bags for blowing, made from newspaper or wood waste and treated with a fire retardant.


A temperature scale on which water freezes at 0 degrees and boils at 100 degrees

Central Heating System

This refers to the primary heating sys­tem of the dwelling unit including the heat producing appliance, the return and supply system for heat distribution.


Recognition by an independent person or group that someone can competently complete a job or task, frequently demonstrated by passing an exam.

Certified Renovator

A person authorized by the EPA to perform repair and renovation projects that disturb lead-based paint.


This term means the amount of cubic feet per minute of air moving through a structure and measured at 50-pascal pres­sure.


The cubic feet of air flowing through a house from indoors to outdoors during typical, natural conditions. This fig­ure can be roughly estimated using a blower door.

CFM - Cubic Feet per Minute

Usually seen as CFM 50, cubic feet per minute of air movement due to 50 pascal house/outdoor pressure differential.


Cavity within a building with a purpose of conveying pipes, ducts, etc. through the building. Chaseways, such as plumbing walls, are common sites for air leakage.


A building component designed for the sole purpose of assuring combustion by-products are exhausted to the exte­rior of the building.

Chimney connector

A pipe that connects a fuel-burning appli­ance to a chimney. Also see vent connector.

Chimney Flue

A passageway in a chimney for conveying com­bustion gases to the outdoors.

Chimney Chase

Typically refers to the cavity between the chim­ney and the framing and other building materials that surround the chimney.

Circuit Breaker

A device found in a Circuit Panel Box that com­pletes an electric circuit. This breaker disconnects the circuit from electricity when it senses an overload of current.


The exterior covering or coating on a structure, such as wood siding, stucco, or brick veneer.

Clean and Tune (C&T)

A procedure performed on a heating or cooling system by a qualified technician to optimize its effi­ciency.


An opening in a chimney (usually at its base) to allow inspection and the removal of ash or debris.


Allowable distances between heat-producing appli­ances, chimneys, or vent systems and combustible surfaces.

Climate zone

An area with a prevailing climate that distin­guishes it from other areas by parameters such as temperature, rainfall, and humidity.


Any set of standards set forth and enforced for the pro­tection of public health and humidity.

Circuit breaker

A device that automatically disconnects an electrical circuit from electricity under a specified or abnormal condition of current flow.

Co-efficient of Performance (COP)

A heat pump or air condi­tioner's output in watt-hours of heat moved divided by watt-hours of electrical input.


A snake-like piece of copper tubing surrounded by rows of aluminum fins that clamp tightly to the tubing and aid in heat transfer.

Coil Stock

Sheet metal packaged as a coil in various widths.

Cold Air Return (return side)

Ductwork through which house air is drawn for reheating during a furnace's cycle.

Cold roof

The condition in which the roof temperature is equal­ized from top to bottom by roof ventilation and/or roof insula­tion.

Collar beam

A horizontal piece in roof framing that provides structural strength by connecting opposite rafters.

Color rendering index (CRI)

A measurement of a light source's ability to render colors the same as sunlight. CRI has a scale of 0 to 100.

Color temperature

A measurement of the warmness or coolness of a light source in the Kelvin temperature scale.


A vertical building support usually made of wood or steel.


Means something will burn, although not neces­sarily readily.

Combustible gas leak detector

 A device for determining the presence and general location of combustible gases in the air.


The act or process of burning. Oxygen, fuel, and a spark must be present for combustion to occur.

Combustion air

Air that chemically combines with a fuel during the combustion process to produce heat and flue gases, mainly carbon dioxide and water vapor.

Combustion Analyzer

A device used to measure and analyze combustion gases for efficiency and safety in heating units.

Combustion Appliance

 Any appliance in which combustion occurs.

Combustion Appliance Zone (CAZ)

The closed space or area that holds one or more combustion appliances.

Combustion Appliance Zone (CAZ) testing

Diagnostics per­formed to ensure that combustion appliances work properly and that house pressures allow combustion gases to vent.

Combustion Byproducts

Gases, vapors, and particulates pro­duced whenever carbon-based fuels such as gas, oil, kerosene, wood, or charcoal are burned.

Combustion Chamber

The area inside the heat exchanger where the flame burns

Combustion efficiency

Synonymous with steady-state efficiency.

Combustion gases

Combustion byproducts.


The process of testing and adjusting building mechanical systems.

Common vent

The portion of the vent or chimney through which passes products of combustion from more than one appliance.

Compact Fluorescent Lamp (CFL)

A small fluorescent light engineered to fit in an Edison base of an incandescent fixture.


Demonstrated ability to perform a job or task.


A motorized pump that compresses the gaseous refrigerant and sends it to the condenser where heat is released

Concentrically Constructed Direct-Vent

A direct-vent appli­ance that has an exhaust-gas vent and a combustion-supply-air vent arranged in a concentric fashion: one pipe is inside the other with a space between the walls of each.


Vapor condensed back to a liquid. For example: water or refrigerant.

Condensate Receiver

A tank for catching returning condensate water from a steam heating system.


When a gas turns into a liquid as it cools, it con­denses. When a gas condenses into a liquid it releases heat.


The coil in a refrigeration system where the refriger­ant condenses and releases heat.

Condensing furnace

A high-efficiency furnace that removes latent heat from combustion gases by condensing water vapor out of the combustion gases.


Intentionally heated or cooled areas of a building

Conditioned Air

Air that has been heated, cooled, humidified, or dehumidified to maintain comfort.

Conditioned space

For energy purposes, space within a building that is provided with heating and/or cooling equipment or sys­tems, or communicates directly with a conditioned space. For mechanical purposes, an area, room or space being heated or cooled by any equipment or appliance.


The quantity of heat, in BTUs, that flows through one square foot of material in one hour, when there is a one degree Fahrenheit temperature difference between both sur­faces. Conductance values are given for a specific thickness of material.


Conduction is the transfer of heat through a mate­rial by molecular movement. Reducing heat loss through con­duction can include the installation insulation in wall, ceiling, and floor cavities, insulation of hot water tanks, creating ther­mal breaks in window and door framing, and sealing of bypasses and other sources of air movement.

Conductive heat flow

Transfer of heat through a solid homoge­neous material.


The quantity of heat that flows through one square foot of homogeneous material, one inch thick, in one hour, when there is a temperature difference of one degree Fahr­enheit between its surfaces.

Confined Space

A space, defined for the purpose of evaluating combustion air, with a volume of less than 50 cubic feet per 1,000 BTU per hour of the total input rating of all combustion appliances installed in that space.


Any for-profit, not-for-profit, or government entity that provides services under contract, not as employees of the purchasing agency.


Difference in brightness measured by the relationship between an object’s brightness and the brightness of its back­ground.

Control Circuit

An electrical circuit that activates or deactivates a power circuit or opens and shuts a valve.


The transfer of heat caused by the movement of a fluid like water or air. When a fluid becomes warmer it becomes lighter and rises.

Convective Loop

Heat flow resulting from airflow caused by temperature differences between surfaces.

Cooling Load

The maximum rate of heat removal required of an air conditioner when the outdoor temperature and humidity are at the highest expected level.

Core competencies

Essential skills for weatherization workers, defined by the Weatherization Trainers Consortium.

Cost Effective

Having an acceptable payback, return-on-invest­ment, or savings-to-investment ratio.

Crawl Space

The low space beneath the ground floor of a build­ing that gives workers access to wiring and plumbing.

Crew Leader

A crew leader is a residential energy professional who is responsible for supervising the retrofitting activities specified in the scope of work.

Critical Framing Juncture

An intersection of framing members and envelope components that require special attention during prep and installation of insulation.

Cross Section

A view of a building component drawn or imag­ined by cutting through the component.

Crosswise floor joist configuration

 home joist configuration where the main duct is located beneath the floor joists and con­nected by boots to the sub-floor.

Cubic Foot Per Minute (CFM)

A measurement of air movement past a certain point or through a certain structure. See also CFM50 and CFMn.

Curtain Wall

A wall between columns and beams that supports no weight but its own


A rectangular groove cut into wood.


One million BTUs or 10 therms.


The wood material installed under roofing material to support the roofing.


Removing or retiring equipment from active service including disposing of hazardous material in an approved way.

Deferral of services

Postponement or denial of weatherization services to the client.   


The removal of water from the air. Excess humidity can cause mold.

Degree Days (DD)

A measure of outdoor temperature calcu­lated by adding the temperature differences between an indoor temperature of 65°F and the daily average outdoor temperature for a one-year period.

Delta T

Temperature difference.


The peak need for electrical energy. Some utilities levy a monthly charge for demand.

Demand Side Management (DSM)

The planning and imple­mentation of those utility-sponsored conservation of electricity or gas.

Dense Packing

Blowing insulation with sufficient force to create a high density to reduce settling and minimize air leakage and air convection.


The weight of a material divided by its volume, usually measured in pounds per cubic foot.

Depressurization Tightness Limit (DTL)

A calculation proce­dure, expressed in units of CFM50, performed to estimate the building tightness level at which combustion appliances might backdraft when the house is under conditions of worst-case depressurization. The DTL sets a low limit for air sealing that may or may not be lower than the BTL for the same house.


Cause to have a lower pressure or higher vacuum with respect to a pressure reference point such as the outdoors.


A liquid or solid material used to absorb water or water vapor.

Design Temperature

A high or low temperature used for design­ing heating and cooling systems when calculating the building load.

Desk Monitoring

Monitoring activities performed through review of paperwork.


A heat exchanger that removes the superheat from a compressed refrigerant and transfers that heat to another fluid, usually water.

Dew point

The warmest temperature of an object in an environ­ment where water condensation from the surrounding air would form on that object.


Movement of water vapor through a material as a function of the vapor pressure across and the vapor permeability of the material.

Dilution air

Air that enters through the dilution device-an opening where the chimney joins to an atmospheric-draft com­bustion appliance

Dilution Device

A draft diverter, draft hood, or barometric draft control on an atmospheric-draft combustion appliance.

Direct current

An electric current flowing in only one direction.

Direct Leakage

Air enters and exits at same location; occurs at direct openings to outdoors.

Direct-vent appliance

A combustion appliance for which all combustion gases are vented to the outdoors through an exhaust vent pipe and all combustion supply air is supplied to the com­bustion chamber from the outdoors through a separate, dedi­cated supply-air pipe.

Discount rate

The interest rate at which expected future cash flows can be discounted. It includes both the present value and fuel escalation rate, and is used to account for the time value of money and the changing price of fuels.

Distribution system

A system of wires, pipes, or ducts that dis­tributes energy.


The United States Department of Energy.

Domestic hot water (DHW)

Refers to a separate, closed system to heat potable (drinkable) water and supply it to the dwelling unit for washing, bathing, etc.

Dominant duct leakage

To measure either dominant supply or return leaks in a forced-air distribution system by measuring house pressure.

Door casing

A wooden trim around doors that covers the seam between the jamb and the wall.

Door stop

The wood trim fastened to the inside of the jamb that positions the door within the jamb and into the latching mecha­nism.


A framed structure projecting above a sloping roof sur­face, and normally containing a vertical window.

Double-hung window

Double-hung windows have operable upper and lower sashes that slide vertically in a channel. Upper sashes are often painted shut.


Airflow configuration in a furnace where cool air is taken from above and discharged as warm air from the bottom.

Downflow furnace

Furnace type where the blower is located at the top of the furnace cabinet and air is forced downwards across the heat exchanger and into the ducts located in the belly cavity


Away from the source of the flow.


A pressure difference that causes combustion gases or air to move through a vent connector, flue, chimney, or combustion chamber.

Draft diverter

A device located in gas appliance flue pipe. Used to moderate or divert draft that could extinguish the pilot or interfere with combustion.

Draft fan

A mechanical fan used in a venting system to aug­ment the natural draft in gas- and oil-fired appliances. These electrically operated, paddle-fan devices are installed in vent connectors.

Draft gauge

Device for testing chimney draft.

Draft hood

See draft diverter.

Draft inducer

A fan that depressurizes the combustion chamber or venting system to move combustion products toward the out­doors.

Draft regulator

A self-regulating damper attached to a chimney or vent connector for the purpose of controlling draft.

Drainage plane

A space that allows water storage and drainage in a wall cavity, adjacent to or part of the water-resistive barrier.

Dropped down belly

 home configuration where a hump is formed in the floor by the main duct running in the center.

Dropped soffit

A lowered part of the ceiling in a home.


Gypsum interior wallboard used to produce a smooth and level interior wall surface and to resist fire. Also called gyp­sum wall board or sheetrock.

Dry bulb temperature

Normal ambient air temperature mea­sured by a thermometer.

Duct blower

A blower-door-like device used for testing duct leakiness and air flow.

Duct board

Rigid board composed of insulation material with one or both sides faced with a finishing material.

Duct boot

Transition piece that connects the main duct to the floor and is often vulnerable to failure.

Duct-induced pressure differences

Pressure differences between rooms in a building caused by the ducted air delivery system, can be due to supply ducts, return ducts, or both.

Duct zone

A building space or cavity that contains heating or cooling ducts.


Any structure which consists of two separate dwelling units in one building.

Dwelling unit

A house, including a stationary mobile home, an apartment, a group of rooms, or a single room occupied as sepa­rate living quarters.


The part of a roof that projects beyond its supporting walls (See - Soffit)

Eave chute

Device that maintains air space between the insula­tion blanket and the roof sheathing and prevents insulation from clogging eave vents.

Eave vent

Vent opening located in the soffit under the eaves of a house to allow the passage of air through the attic and out the roof vents.


The ratio of output divided by input


The number of lumens produced by a watt used for lighting a lamp. Used to describe lighting efficiency.

Egress window

A window with a defined opening size for the purpose of fire escape.


A characteristic of a material that is flexible and permits movement.

Elastomeric coating

Polymeric material, such as acrylic, that is used to repair roof leaks and to reduce solar heat gain.

Electric service

The electric meter and main switch, usually located outside the building.


Describes controls where switching is per­formed by an automatic mechanical device like a bimetal or bulb-and-bellows.

Emergency heat

A heating device that doesn’t require electricity used during an emergency. Or electric-resistance heating ele­ments used for heating in case a heat pump’s compressor fails.


The rate that a material emits radiant energy from its surface. Also called emissivity.


Any covering or coating that acts as a barrier between the hazard, such as lead-based paint, and the indoor environment.


The building shell. The exterior walls, floor, and roof assembly of a building. Also referred to as building envelope.


A quantity of heat or work

Energy audit

The process of identifying energy conservation opportunities in buildings.

Energy auditor

One who inspects and surveys the energy use of buildings in order to promote energy conservation.

Energy conservation measures (ECM)

Building components or products installed to reduce the building's energy consumption.

Energy consumption

The conversion or transformation of potential energy into kinetic energy for heat, light, electricity, etc.

Energy education

The process used by WAP staff to inform cus­tomers of the ways they can further reduce energy consumption through altering their behavioral patterns. The most effective protocol includes multiple interaction and reinforcement with the household residents and use of a negotiated and written action plan.

Energy efficiency

Term used to describe how efficiently a build­ing component uses energy.

Energy efficiency ratio (EER)

A measurement of energy effi­ciency for room air conditioners. The EER is computed by dividing cooling capacity, measured in British Thermal Units per hour (Btuh), by the watts of power. (See - Seasonal Energy Efficiency Rating or SEER)

Energy factor

The fraction of water heater input remaining in 64 gallons of hot water extracted from a water heater.

Energy Information Administration (EIA)

Section of the U.S. Department of Energy providing statistics, data, and analysis on resources, supply, production, and consumption for all energy sources.

Energy rater

Evaluates the energy efficiency of a home and assigns a relative performance score, a certification received from HERS (Home Energy Rating System).

Energy-recovery ventilator (ERV)

A ventilator that recovers latent and sensible energy from the exhaust airstream and imparts it to the incoming airstream.


The internal heat of a material measured in Btus per pound.


Heat unavailable to a closed thermodynamic system during a heat transfer process.


The building shell. The exterior walls, floor, and roof assembly of a building. Also referred to as building enclosure.

Environmentally Sensitive

Highly susceptible to adverse effects of pollutants.

EPA, U.S. Environmental Protection Agency

EPA protects human health and safeguards the natural environment - air, water, and land upon which life depends.

Equivalent Leakage Area (ELA)

Calculation, in square inches, of the total area of all holes and cracks in a structure. The leakage area is then accumulated to represent one total leakage point.

Equivalent length

The length of straight pipe or duct that has equivalent resistance to a pipe or duct fitting. Used for piping and duct design.

Equivalent duct length (EDL)

A measure of how much static pressure an exhaust fan has to overcome.

Equivalent leakage area (ELA)

Calculation, in square inches, of the total area of all holes and cracks in a structure. The leakage area is then combined to represent one total leakage point.


The change that occurs when a liquid becomes a gas. Evaporation is the key process in the operation of air condi­tioners and evaporative coolers. Evaporation is a cooling pro­cess.

Evaporative cooler

A device for cooling homes in dry climates by humidifying and cooling incoming air by the evaporation of water.


The heat transfer coil of an air conditioner or heat pump that cools the surrounding air as the refrigerant inside the coil evaporates and absorbs heat.

Excess air

Air in excess of what is needed for combustion.


This term describes the movement of air out of a building. Often refers to warm air leaving a building due to pres­surization, infiltration, wind, stack effect, and/or convective flow.

Expanded polystyrene

White polystyrene insulation.

Expanding foam

An insulation product designed to expand and harden upon contact with the air. Available in canisters with spray nozzles that make it easy to apply foam in a wide variety of situations.

Expansion valve

A valve that meters refrigerant into the evapo­rator.


A temperature scale used in the United States and a few other countries. On the Fahrenheit scale, water boils at 212 degrees and freezes at 32 degrees.

Fan-assisted combustion

A combustion appliance with an inte­gral fan to draw combustion supply air through the combustion chamber.

Fan control

A bimetal thermostat that turns the furnace blower on and off as it senses the presence of heat.

Fan-off temperature

In a furnace, the supply air temperature at which the fan control shuts down the distribution blower.

Fan-on temperature

In a furnace, the supply air temperature at which the fan control activates the distribution blower.

Federal Energy Management Program (FEMP)

A program of DOE that implements energy legislation and presidential direc­tives. FEMP provides project financing, technical guidance and assistance, coordination and reporting, and new initiatives for the federal government.

Feeder wires

The wires connecting the electric meter and main switch with the main panel box indoors.


Window and door openings in a building's wall.


A fibrous material made by spinning molten glass used as an insulator and heat loss retardant.

Field testing

Assessment of a trainee's abilities conducted on-site, rather than in a classroom.

Fill Tube

A plastic or metal tube used for its stiffness to blow insulation inside a building cavity.

Fin comb

A comb-like tool used to straighten bent fins in air conditioning coils.

Final inspection

An evaluation of a weatherization job after its completion.

Finished attic

An attic that was converted to living space by the construction of dormers and knee walls.

Finned tube

A length or coil of pipe with heat transfer fins attached for water-to-air heat transfer.

Fire barrier

A tested building assembly, designed to contain a fire for a particular time period: typically 1-to-4 hours.


Building materials installed to resist the free pas­sage of flame to other areas of the building through concealed spaces.

Fire resistance

The property of materials or their assemblies that prevents or retards the passage of excessive heat, hot gases or flames under conditions of use.

Fire resistance rating

The period of time a building element, component or assembly maintains the ability to confine a fire, continues to perform a given structural function, or both.

Fire stop

Framing member designed to stop the spread of fire within a wall cavity.


A structural wall between buildings designed to pre­vent the spread of a fire.

Firing chamber

The compartment inside an oil-burning furnace or boiler where the electrodes ignite the air/atomized oil mix­ture.

Flame impingement

The striking of flame against an object.

Flame rectification

A modern method of flame sensing, which uses the flame itself as a conductor in the flame-safety circuit.

Flame-retention head burner

A higher efficiency burner in an oil furnace that produces a hotter flame and operates with a lower air flow, thus reducing loss up the chimney.

Flame roll-out

Fuel gas combustion process occurring outside the normal combustion area of a combustion appliance.

Flame safety control

A control device used to stop the flow of fuel to the burner assembly in the event of no ignition.

Flame spread

The broadening or spreading of a flame.


The rating for building materials that will burn readily when exposed to a flame.


Combustible; readily set on fire.


Waterproof material used to prevent leakage at inter­sections between the roof surface at walls or penetrations.

Floor Joists

The framing members that support the floor area.


The channel of pipe used to control air flow of combustion gases.

Flue gas

Gases arising from the combustion of fuels, mainly consisting of carbon dioxide. Fuel gas normally contains pollut­ants, such as carbon dioxide, nitrogen oxide, sulfur dioxide, and dust.

Flush flange

A window designed to provide a finished exterior appearance over a flat exterior surface like stucco.

Foam board

Plastic foam insulation manufactured most com­monly in 4'x8' sheets in thickness of 1/4” to 3".

Foam compatible adhesive

Adhesive that is manufactured for the purpose of safely adhering to foam.

Foot candle

A measure of light striking a surface.


The part of a foundation system that actually transfers the weight of the building to the ground.

Forced draft

A vent system for which a fan installed at the com­bustion appliance moves combustion gases to the outdoors with positive static pressure in the vent pipe. Because of this positive pressure, the vent connector must be air-tight.


Easily broken into small fragments or reduced to pow­der, as with asbestos

Frost line

The maximum depth of the soil where water will freeze during the coldest weather.

Fuel escalation rate

Annual escalation rate of fuel prices based on the annual energy price forecasts of DOE's Energy Informa­tion Administration.


An appliance for heating a medium to distribute heat throughout the dwelling unit.

Furnace blower

A part of the furnace that produces a current of air. Often referred to as the “blower” or “squirrel cage.”

Furnace plenum

An air chamber that gets filled directly by a large blower that is above, below, or adjacent to it.


Thin wood strips fastened to a wall or ceiling surface as a nailing base for finish materials.


A current carrying element that melts if too much current flows in an electric circuit.


The triangular section of an end wall formed by the pitch of the roof.

Gable Roof

A roof shape that has a ridge at the center and slopes in two directions.

Gable vent

A screened vent installed at or near the peak of a roof gable that allows warm attic air to escape.

Gallons per minute (GPM)

The unit for measuring water flow, frequently for showers.


Elastic strip that seals a joint between two materials.

General heat waste

Weatherization materials that DOE has determined to be generally cost-effective. DOE must specifically approve these measures.


Any brightness or brightness relationship that annoys, distracts, or reduces visibility.

Glass load factor

A number combining glass's solar heat trans­mission and its heat conduction. Used for cooling load calcula­tions.


Glass installation. Pertaining to glass assemblies or windows

Glazing Compound

A flexible, putty-like material used to seal glass in its sash or frame.


The pitch of a slope such as a roof or a hill.


The individual or organization that receives a grant.

Gravity furnace

A central heating system that uses natural grav­ity to distribute heat throughout the dwelling unit as opposed to forced circulation, pumps, or circulation blowers.

Ground fault circuit interrupter (GFI or GFCI)

An electrical connection device that breaks a circuit if a short occurs. These are required for all exterior use of electrical equipment, or when an electrical outlet is located near a water source.

Ground-moisture barrier

Most crawl spaces require ground-moisture barriers to prevent the ground from being a major cause of moisture problems. The ground under a building is the most potent source of moisture in many buildings, especially those built on crawl spaces.


A metal or wood plate added to the surface of a joint to strengthen the connection.

Gypsum board

A common interior sheeting material for walls and ceilings made of gypsum rock powder packaged between two sheets of heavy building paper. Also called drywall, sheet­rock, gyprock, or gypboard.

Habitable space

A building space intended for continual human occupancy. Examples include areas used for sleeping, dining, and cooking, but not bathrooms, toilets, hallways, storage areas, closets, or utility rooms. See occupiable space and conditioned space.

Hallway return or hallway return system

A type of mobile home air distribution system. The mobile home heating or cooling system receives return air through a central trunk line beneath the hallway.


 A rectangular hole in a horizontal building assembly like a floor or ceiling that allows access

Hazardous Material

A particular substance that is considered a danger to the client or crew.


Foot pounds of mechanical energy per pound of fluid cre­ated by a pump to overcome gravity or friction.

Head jamb

Groove at the top of the window that allows the window sashes to slide into place and sit inside the window frame.

Health and safety (H&S)

Provision included in a 1976 law change for the Weatherization Assistance Program. WAP now considers the health and safety of low-income families, as well as reducing their energy costs.


Molecular movement

Heat anticipator

A device in a thermostat that causes the ther­mostat to turn off before room temperature reaches the thermo­stat setting, so that the house doesn’t overheat from heat remaining in the heater and distribution system after the burner shuts off.

Heat capacity

The quantity of heat required to raise the tem­perature of 1 cubic foot of a material 1 degree F.

Heat exchanger

The device in a heating unit that separates the combustion chamber from the distribution medium and trans­fers heat from the combustion process to the distribution medium.

Heat gains

Term used to mean unwanted heat that accumulates in homes, making mechanical cooling desirable or necessary.

Heat loss

The amount of heat escaping through the building shell as measured for a specific period of time (month, year, etc.)

Heat pump

A type of heating/cooling unit, usually electric, that uses a refrigerant fluid to heat and cool a space.

Heat-recovery ventilator

A central ventilator that transfers heat from exhaust to intake air.

Heat rise

The number of degrees of temperature increase that air is heated as it is blown over the heat exchanger. Heat Rise equals supply temperature minus return temperature.

Heat transmission

Heat flow through the walls, floor, and ceil­ing of a building, not including air leakage.

Heat transfer coefficient

See U-factor.

Heating degree day(s) (HDD)

See: Degree days

Heating Load

The maximum rate of heat conversion needed by a building during the very coldest weather.

Heating seasonal performance factor (HSPF)

Rating for heat pumps describing how many Btus they transfer per kilowatt-hour of electricity consumed.

High-efficiency particulate air (HEPA) vacuum

HEPA vacuum means a vacuum cleaner which has been designed with a high-efficiency particulate air (HEPA) filter as the last filtration stage.

High limit

A bimetal thermostat that turns the heating element of a furnace off if it senses a dangerously high temperature.


The metal objects that attach your door to the jamb, normally with screws. They can be made from brass, steel, iron, or other metals.

Hip roof

A roof with two or more contiguous slopes, joined along a sloping “hip.”

Home energy index

The number of BTUs or kWh of energy used by a home, divided by its area of conditioned square feet.

Home energy rating systems (HERS)

A nationally recognized energy rating program that give builders, mortgage lenders, sec­ondary lending markets, homeowners, sellers, and buyers a pre­cise evaluation of energy losing deficiencies in homes.

Home heating index

The number of Btus of energy used by a home divided by its area in square feet, then divided by the number of heating degree days during the time period.

HOME Program

A program created under Title II (the Home Investment Partnership Act) of the National Affordable Hous­ing Act of 1990. Provides funds for states to expand the supply of decent and affordable housing for low-income people. This program can be easily coordinated with a state's WAP efforts.

Home Ventilating Institute (HVI)

A non-profit association of manufacturers of residential ventilating products offering a vari­ety of services including test procedures, certification and verifi­cation programs for products, and market support.

Hot roof

An unventilated roof with insufficient insulation to prevent snow melting on the roof and the creation of ice dams.

House as a system

The concept that many components of a house interact, affecting the home’s comfort and performance.

House depressurization limit

A selected indoor negative pres­sure; expressed in Pascals, immediately around vented combus­tion appliances that use indoor air for combustion supply air.

House pressure

The difference in pressure between the indoors and outdoors measured by a manometer.

House wrap

A generic term for the modern version of the building’s water-resistive barrier.


U.S. Department of Urban Housing and Development


An automatic control that switches a fan, humidi­fier, or dehumidifier on and off to control relative humidity.

Humidity ratio

Same as “absolute humidity.” The absolute amount of air’s humidity measured in pounds or grains of water vapor per pound of dry air.


Heating, Ventilation, and Air-Conditioning System. All components of the appliances used to condition interior air of a building.

Hydronic system

A heating system that uses hot water or steam as the heat-transfer fluid. Commonly called a hot-water heating system.


A tool for measuring relative humidity. A psy­chrometer, which uses two thermometers, one with a dry bulb and one with a wet bulb, is a simple hygrometer.


Indoor Air Quality. The quality of indoor air relative to its acceptability for healthful human habitation.


A rolled or extruded metal beam having a cross section resembling an I.

IC rated

Insulation Contact rating for light fixtures. IC housings may be in direct contact with fibrous insulation.

Ice dam

Ice that forms at the roof eaves during differential freezing and thawing.


International Energy Conservation Code

Ignition barrier

A material installed to prevent another mate­rial, often plastic foam, from catching fire.


The light level measured on a horizontal plane in Foot Candles

Inaccessible cavity

An area that is too confined to enter and/or maneuver in by an average installer/technician.

Incandescent light

The common light bulb found in residential lamps and light fixtures and known for its inefficiency.

Inches of Water Column (IWC)

A non-metric unit of pressure difference. One IWC is equal to about 0.004 Pascals.

Incidental repairs

Under DOE rules, this term refers to the repairs on a dwelling unit necessary for the effective perfor­mance or preservation of the allowable energy conservation measures to be installed.

Indirect leakage

When air leaks into the home at one point, and out at a different opening. Indirect leakage is more difficult to find, and is associated with interior bypasses or chaseways of a home's interstitial cavities.

Indoor air quality (IAQ)

The quality of indoor air relative to its acceptability for healthful human habitation.

Induced draft

A vent system or combustion appliance for which a fan, installed at or very near the termination point of the appliance or the vent pipe, moves the combustion gases.


Infiltration refers to the movement of air into a building through cracks and penetrations in the building enve­lope.


Pertaining to heat rays emitted by the sun or warm objects on earth.

Infrared camera

A special camera that “sees” temperature dif­ferences on surfaces, allowing the user to determine if a building assembly is insulated properly. This instrument is also useful for detecting air leakage if used with a blower door.

Infrared thermography

The science of using infrared imaging to detect radiant energy or heat loss characteristics of a building.

Input rating

The measured or assumed rat at which an energy-using device consumes electricity or fossil fuel.


The amount of solar radiation striking a surface.


A weatherization worker responsible for quality con­trol or quality assurance by making final inspections and in-progress inspections.

Inspection gap

A gap in foundation insulation left for the pur­pose of inspecting for insect infestation.

Insulated flex duct

A round duct composed of two flexible plas­tic tubes with tubular insulation between the two.

Insulated glass

Two or more glass panes spaced apart and sealed in a factory.


A material used to resist heat transmission.

Insulation dam

A material that prevents fibrous insulation from flowing into an area where it isn’t necessary or wanted.

Insulation restrainer

A flexible material, such as netting or fab­ric, use to hold blown fibrous insulation in place.

Insulation shield

A fire-barrier erected around a heat producing device to prevent insulation from covering or contacting the heat-producing device.

Insulated glass unit (IGU)

Two or more glass panes spaced apart and sealed in a factory,.

Intentionally conditioned

Conditioned by design and fitted with radiators, registers, or other devices to maintain a comfortable temperature.

Intermediate zone

A zone located between the building’s condi­tioned space and the outdoors, like a crawl space or attic.

Intermittent ignition device (IID)

A device that lights the pilot light on a gas appliance when the control system calls for heat, thus saving the energy wasted by a standing pilot.

Internal gains

The heat generated by bathing, cooking, and operating appliances, that must be removed during the summer to promote comfort.

International Association of Plumbing and Mechanical Officials (IAPMO)

The industry trade group that develops the Uniform Mechanical Code and the Uniform Plumbing Code.

International Codes Council (ICC)

An international non-gov­ernmental organization for developing building safety, fire pre­vention, and energy efficiency codes (I-codes).

International Fuel Gas Code (IFGC)

Code that addresses the design and installation of fuel gas systems and gas-fired appli­ances through requirements that emphasize performance.

International Residential Code (IRC)

Interstitial Space

Space between framing and other building components.


Air moving into and out of insulation without going through the wall or ceiling assembly.

Jalousie windows

A type of window usually associated with homes with two or more panes of glass that pivot on a horizon­tal axis.


The side or top piece of a window or door frame.

Jamb clips or plates

Structural devices used to fasten a block-frame window to its opening.


A horizontal wood framing member that supports a floor or ceiling.


A unit of energy. One thousand joules equals 1 BTU.


A slit made by cutting, often with a saw.


A unit of electric power equal to 1000 joules per sec­ond or 3412 Btus per hour.


The most commonly used unit for measuring the amount of electricity consumed over time; one kilowatt of elec­tricity supplied for one hour. A unit of electric energy equal to 3600 kilojoules.

Knee wall

A short wall, often under three feet in height. The term is derived from the association with the vertical location of the human knee. Knee walls are common in old houses that are typically not a full two stories in height, in which the ceiling on the second floor slopes down on one or more sides. These houses are sometimes referred to as one and a half stories.

Knee-wall attic

An triangular attic with short walls, usually under three feet in height.

Knob-and-tube wiring

Early standardized method for electrical wiring in homes consisting of insulated copper conductors sup­ported by porcelain knobs and tubes (when passing through framing members).


A light bulb.

Latent heat

The amount of heat energy required to change the state of a substance from a solid to a liquid, or from a liquid to a gas.


A support for plaster, consisting of thin strips of wood, metal mesh, or gypsum board.

Lawrence Berkeley National Laboratory (LBNL)

Member of the national laboratory system supported by DOE though its Office of Science. It conducts unclassified research across a wide range of scientific disciplines.

Lead-Safe Work Practices (LSW)

Work practices required by DOE for pre-1978 homes when the weatherization work will disturb more than 2 square feet of painted surface in an interior room, 10 percent of a small component such as a baseboard or door casing, and/or when the work will disturb more than twenty square feet of painted exterior surface.

Leadership in Energy and Environmental Design (LEED)

A building certification system developed by the U.S. Green Build­ing Council.

Leakage ratio

Measurement of total square inches of air leakage area per 100 feet of building envelope surface area.

Light quality

The relative presence or absence of glare and brightness contrast. Good light quality has no glare and low brightness contrast.

Local agency

Also referred to as the subgrantee, contractor, ser­vice delivery network member, or local service provider, a local agency is a nonprofit organization or unit of local government responsible for providing WAP services in a specified political subdivision.

Loose fill insulation

Fibrous insulation in small fibers that are blown into a building assembly using a blowing machine.

Low-flow rings

Part of a blower door that forces air past the sen­sors fast enough so that a reliable reading can be obtained.


Short for “low emissivity”, which means the characteris­tic of a metallic glass coating to resist the flow of radiant heat.

Low expanding foam

Liquid-applied form that expands 20-30 times its liquid size.

Low water cutoff

A float-operated control for turning the burner off if a steam boiler is low on water.


A unit of light output from a lamp.


A light fixture.

Main panel box

The electric service box containing a main switch, and the fuses or circuit breakers located inside the home.

Make-up air

Air supplied to a space to replace exhausted air.


A tube with one inlet and multiple outlets, or multi­ple inlets and one soutlet.


A differential gauge used for measuring pressure.

Manual J

Load calculation that allows the user to properly size HVAC systems for single-family-detached homes, small multi-unit structures, condominiums, town houses, and manufactured homes.

Manufactured home

A home or a “double-wide” structure. Transportable homes that are quick and cheap to build. Another name for home.

Manufactured Home Energy Audit (MHEA)

A tool to predict manufactured home energy consumption and recommend weatherization retrofit measures, accounting for local weather conditions, retrofit measure costs, and fuel costs.


A thick creamy substance used to seal seams and cracks in building materials.


Stone, brick, or concrete block construction.

Materials safety data sheet (MSDS)

A sheet containing data regarding the properties of a particular substance, intended to provide workers with procedures for handling or working with that substance in a safe manner, including information such as physical data, toxicity, health effects, first aid, storage, disposal, and protective equipment.

Mean radiant temperature (MRT)

The area-weighted mean temperature of all the objects in an environment.

Mechanical draft

A combustion appliance with induced draft of forced draft.

Meeting rails

The rail of each sash that meets a rail of the other when the window is closed.


A barrier that separates two environments. Mem­branes may be permeable to the flow of air, water, and other flu­ids or particles.


A very localized climatic area, usually of a small site or habitat.


Fungi that colonize organic building materials.


To make less severe or to mollify.

Mobile home belly

Part of a home that contains the insulation, duct system, and plumbing. It is enclosed by the sub- and fin­ished floor, with a rodent barrier underneath.

Mobile Home Energy Audit (MHEA)

A software tool that pre­dicts manufactured home energy consumption and recom­mends weatherization retrofit measures.

Moisture meter

An instrument for measuring the percentage of water in a substance.


A growth of minute fungi forming on vegetable or animal matter and associated with decay or dampness.


The process through which a person, frequently a rep­resentative of a State or Federal agency, visits completed units to ensure that weatherization funding is spent appropriately.


The process through which a person, frequently a representative of a State or Federal agency, visits completed units to ensure that weatherization funding is spent appropri­ately.


A mixture of sand, water, and cement used to bond bricks, stones, or blocks together.


A recessed area cut into the wood framing member where a hinge or wood tongue fits.


Materials Safety Data Sheet.

Mud sill

A wood component attached to the foundation of a building that creates a means of attaching various components of the framing to the foundation.


Vertical framing members that don't run the full length of the door.

Multifamily (MF) housing

A building with five or more residen­tial units.

Mushroom vent

A vent that has at the top of a vertical shaft a broad rounded cap that can be screwed down to close it.


A factor used to convert blower-door measurements taken at CFM50 to CFMnatural, the amount of air leakage that occurs naturally. N ranges from 9 to 35.

Nail fin

Semi-flexible strips of metal or plastic used to attach a window frame to a rough opening.

Nailing Flange

An extrusion attached to the window and used to attach the unit to the opening.

National Association for State Community Services Programs (NASCSP)

Assists States in responding to poverty issues. NASCSP members are state administrators of the Community Services Block Grant (CSBG) and U.S. Department of Energy's Weatherization Assistance Program (DOE/WAP).

National Bureau of Standards (NBS)

Renamed by the Depart­ment of Commerce as the National Institute of Standards and Technology (NIST).

National Electric Code (NEC)

A safety code regulating the elec­tricity use. The NEC is a product of the National Fire Protection Association.

National Energy Audit Tool (NEAT)

Created by Oak Ridge National Laboratories as a DOE approved audit qualifying for the 40% materials waiver. It is a computerized auditing tool for prioritizing energy conservation measures for houses.

National Fenestration Rating Council (NFRC)

NFRC is a non-profit organization that administers the only uniform, indepen­dent rating and labeling system for the energy performance of windows, doors, skylights, and attachment products.

National Fire Protection Association (NFPA)

Creates and main­tains minimum standards and requirements for fire prevention, training, and equipment, developing and publishing codes and standards such as the NFPA 70, the National Electric Code, and NFPA 54, the National Fuel Gas Code.

National Institute for Occupational Safety and Health (NIOSH)

 A federal agency responsible for conducting research and mak­ing recommendations for the prevention of work-related injury and illness to help ensure safe and healthful working conditions.

Natural draft

Draft that relies on buoyancy heated gases to move combustion gases up a chimney.

Natural gas

A hydrocarbon gas that is usually obtained from underground sources, often in association with petroleum and coal deposits.

Natural Ventilation

Ventilation using only natural air move­ment without fans or other mechanical devices.

Net Free Vent Area (NFVA)

The area of a vent after that area has been adjusted for insect screen, louvers, and weather covering. The free area is always less than the actual area.


An open weave fabric or plastic mesh that supports fibrous insulation.


National Fire Protection Association.

NFPA 211

National Fire Protection Association's Standard for Chimneys, Fireplaces, Vents, and Solid-Fuel-Burning Appli­ances includes installation procedures for vents and chimneys that serve wood-burning stoves and fireplaces.


National Fire Protection Association's Standard for the Implementation of Oil-Burning Equipment, dictating that chimneys must be at least 2 feet higher than any portion of the building within 10 feet.


National Fire Protection Association's National Fuel Gas Code.

Noncombustible material

Materials that pass the test procedure for defining noncombustibility of elementary materials set forth in ASTM E 136.

Nonconditioned space

A space that isn’t heated or cooled.

Non-expanding foam

Spray foam that does not expand. Used in window and door jambs, and other constricted spaces where expanding foam may distort building materials and negatively impact operation.

Non-flame retention head burner

An older type of burner than the “flame retention head burner,” requiring more excess air, which burns less efficiently.


An orifice for spraying a liquid like fuel oil.



Oak Ridge National Laboratory (ORNL)

Laboratory where the Mobile Home Energy Audit (MHEA) software was developed.


People of any age living in a dwelling. Animals are not defined as occupants.

Occupational Safety and Health Administration (OSHA)

An agency of the United States Department of Labor, with a mission to prevent work-related injuries, illnesses, and occupational fatality by issuing and enforcing standards for workplace safety and health.


Off-gassing is the evaporation of volatile chemicals in non-metallic materials at normal atmospheric pressure. This means that building materials can release chemicals into the air through evaporation.


A unit of measure of electrical resistance. One volt can produce a current of one ampere through a resistance of one ohm.

One-part foam

One-part foam comes in spray cans (e.g., Great Stuff) and spray guns with screw-on cans. One-part foam is best suited for filling gaps and holes less than ¾”.

Open-combustion appliance

An appliance that does not have a sealed combustion chamber and may take its combustion air from the surrounding room.

Open-Combustion Heater

A heating device that takes its com­bustion air from the surrounding room air.


A hole in a gas pipe or nozzle fitting where gas or fuel oil exits to be mixed with air before combustion occurs in the heat­ing chamber. The size of the orifice will help determine the flow rate.

Oscillating Fan

A fan, usually portable, that moves back and forth as it operates, changing the direction of the air movement.


Occupational Safety and Health Administration

Output capacity

The useful heat in BTUH that a heating unit produces after accounting for waste.


In reference to furnaces; when too much fuel is being burned, as a response to over-sized fuel nozzles, over-pressur­ization from the pump, etc.


The combination of a substance with oxygen.

Oxygen content

A measure of the amount of oxygen in the air.

Oxygen-depletion sensor

A safety device on a heating unit that shuts off the fuel supply to the combustion chamber when oxy­gen is depleted.

Packaged air conditioner

An air conditioner that contains the compressor, evaporator, and condenser in a single cabinet.

Packaged terminal air conditioner (PTAC)

A self-contained space heating and/or cooling system, usually powered with elec­tricity, commonly found in hotels and apartment buildings.

Packaged terminal heat pump (PTHP)

A self-contained space heating and/or cooling system, frequently installed in a sleeve through the exterior wall of a building, using heat pump tech­nology.


Parts of a door between rails and stiles or mullions.

Parapet walls

A low wall at the edge of a platform, roof or bridge,

Parts per million (ppm)

The unit commonly used to represent the degree of pollutant concentration, where the concentrations are small.

Pascal (Pa)

A unit of measurement of air pressure. One column inch of water equals 247 pascals. Atmospheric pressure (29.92 inches of mercury) is equivalent to 102,000 PA. 2.5Pa = 0.01 inches of water column.

Passive attic venting

Takes advantage of the natural buoyancy of air by providing inlets and outlets low and high on the roof. Warm air rises through higher vents and cooler air is drawn through eave vents as the warm air escapes.

Payback period

The number of years that an investment in energy conservation will take to repay its cost through energy savings.

Performance standard

Specification of the conditions that will exist when a satisfactory job is performed.

Perimeter basement drain

An indoor drain cut into the floor and around the perimeter of a basement or crawl space to inter­cept and remove water from the building interior.


A heat-expanded mineral used for insulation.


A measurement of how much water vapor a material transmits per hour. Specifically: diffusion of 1 grain of water vapor per hour, per square foot, per inch of mercury pressure.

Permeance rating

Number that quantifies the rate of vapor dif­fusion through a material.

Personal fall arrest system

A system used to arrest an employee in a fall from a working level. It consists of an anchor point, con­nectors, a body belt or body harness and may include a lanyard, deceleration device, lifeline, or combinations of these.

Personal protective equipment (PPE)

Accessories such as safety glasses, ear plugs, and respirators worn to protect individuals from workplace hazards.

Phase change

The act of changing from one state of matter to another, for example: solid to liquid or liquid to gas.


Electronic sensing device used to sense flame, daylight, artificial light.

Photovoltaic (PV)

A solid-state electrical device that converts light directly into direct current electricity.


Polyisocyanurate foam insulation.

Picture window

Picture windows have no operable sashes and are used primarily for aesthetics.

Pier and beam foundation

Housing base that uses a concrete footing and pier to support wood beams and floor joists.


A plastic mixture of sand, lime, and Portland cement spread over wood or metal lath to form the interior surfaces of walls and ceilings.

Plastic tie band

A ratcheting plastic band used to clamp flexible ducts to metal ducts or to attach insulation to round metal ducts.


A framing member installed horizontally to which the vertical studs in a wall frame are attached.

Platform framing

A system of framing a building in which floor joists of each story rest on the top plates of the story below or on the foundation sill for the first story, and the bearing walls and partitions rest on the subfloor of each story.


The piece of ductwork that connects the air handler to the main ducts.


Absolutely vertical at a right angle to the earth's surface.


Laminated wood sheeting with layers cross-grained to each other.

Pocket doors

Doors that slide into a wall cavity and are typically very leaky.


A plastic made by the polymerization of ethylene, used in making translucent, lightweight, and tough plastics, films, insulations, vapor retarders, air barriers, etc.

Polyisocyanurate (PIC)

A plastic foam insulation sold in sheets, similar in composition to polyurethane.

Polystyrene insulation

A rigid plastic foam insulation, usually white, pink, green, or blue in color.


A versatile plastic foam insulation, usually yellow in color.


Measure of the void spaces in a material, expressed as either a fraction or a percentage of the total volume of material.

Positive-pressure, supplied-air respirator

Has its own air com­pressor to supply fresh air to the worker, and can use a mask or hood.

Potential Energy

Energy in a stored form, like fuel oil, coal, wood, or water stored at a high elevation


A variable resistor used as a controller or sensor.

Pounds per square inch (psi)

Units of measure for the pressure a gas or liquid exerts on the walls of its container.

Power burner

A burner that moves combustion air at a pressure greater than atmospheric pressure. Most oil-fired burners are power burners. Gas burners used to replace oil burners are usu­ally power burners.

Power vent

A combustion appliance that uses fan-powered draft for venting combustion byproducts.

Prescriptive standard

Specifies in detail the requirements and procedures to be followed rather than specifying a performance outcome.

Present value (PV)

The amount that a future sum of money is worth today given a specified rate of return.


A force encouraging movement of a fluid by virtue of a difference in some condition between two areas.

Pressure balancing

To equalize house or duct pressure by adjust­ing air flow in supply and return ducts. Used on dwellings with forced air heating systems.

Pressure boundary

The surface that separates inside from out­side, in relation to conditioned space within the home. Also called air boundary or air barrier.

Pressure diagnostics

The practice of measuring pressures and flows in buildings to control air leakage, and also to ensure ade­quate heating and cooling air flows and ventilation.

Pressure-equalized rain screen

A space between the water-resis­tive barrier and the cladding in an exterior wall that is con­nected to the outdoors so that there is no pressure difference between the space and the outdoors. This assembly gives supe­rior resistance to wind-driven rain where such weather is com­mon.

Pressure pan

A device used to block a duct register while mea­suring the static pressure behind it.

Pressure-pan testing

One method for determining duct leakage. Uses a pressure pan, manometer, and a blower door to quantify pressure differences and verify improvements after duct sealing.


A control that turns a steam boiler's burner on and off as steam pressure changes.

Pressure-reducing valve

An adjustable valve that reduces the building’s water pressure to provide water to hydronic and steam heating systems.

Pressure-and-temperature relief valve

A safety component required on a boiler and water heater, designed to relieve excess pressure or temperature in the tank.

Primary air

Air mixed with fuel before combustion.

Prime window

The main window installed on the outside wall consisting of fixed or moveable lights that slide on permanently fixed tracks (not to be confused with a storm window).

Priority list

The list or ranking of installation measures devel­oped by a program to produce the most cost effective energy savings results based on a savings to investment ratio calcula­tion.

Propane (liquefied petroleum gas, or LPG)

A colorless, flamma­ble gas occurring in petroleum and natural gas.


An instrument for determining atmospheric humidity by the reading of two thermometers, the bulb of one being kept moist and ventilated.

Psychrometric chart

A chart presenting the physical and ther­mal properties of moist air in graphical form. Used in conjunc­tion with a psychrometer to determine relative humidity, dew point, and other characteristics.


The study of the relationship between air, water vapor, and heat.

Pull-down stairs

Staircase that folds up into the attic until pulled down for use.

Pulley seals

A component of a window sash counterweight sys­tem that helps control the movement of the lower sash.


Framing members that sit on top of rafters, perpendicu­lar to them, designed to spread support to roofing materials.

Quality assurance

The systematic evaluation of a product or service to ensure quality standards are being met.

Quality control (QC)

Review of the final work product to ensure that it was correctly done.


A measurement of thermal resistance for materials and related surfaces.

Radiant barrier

A foil sheet or coating designed to reflect heat flows. Radiant barriers are not mass insulating materials.

Radiant temperature

The surface temperature of objects in a home, like walls, ceiling, floor, and furniture.


Heat energy that is transferred by electromagnetic energy or infrared light, from one object to another. Radiant heat can travel through a vacuum and other transparent materi­als.


A radioactive gas that decomposes into radioactive par­ticles.


A roof beam that follows the roof's slope.

Rain screen

The combination of a water-resistive barrier and a space, used to keep wall assemblies dry in climates with high rainfall.


A person who performs energy ratings. Same as energy rater.

Recovery efficiency

A water heater's efficiency at actually heat­ing water to capacity level without regard to standby or distribu­tion losses.


The ratio of lamination or radiant heat reflected from a given surface to the total light falling on it. Also called reflectivity.

Reflective glass

Glass that has a mirror-like coating on its exte­rior surface to reflect solar heat. The solar heat gain coefficient of reflective glass ranges from 0.10 to 0.40.


Any of various liquids that vaporize at a low tem­perature, used in mechanical refrigeration.


A special fluid used in air conditioners and heat pumps that heats air when it condenses from a gas to a liquid and cools air when it evaporates from a liquid to a gas.


The grille cover over a duct outlet for warm air distri­bution or cold air return and sometimes control the flow.


The replacement of an existing, standard light bulbs with lower wattage energy efficient bulbs like compact fluores­cent lamps.

Relative humidity

The percent of moisture absorbed in the air compared to the maximum amount possible. For instance, air that is completely saturated has 100% relative humidity.


An automatic, electrically-operated switch.

Reset controller

Adjusts fluid temperature or pressure in a cen­tral heating system according to outdoor air temperature.


The property of a material resisting the flow of elec­trical energy or heat energy.


An energy conservation measure applied to an existing building or the action of improving the thermal performance or maintenance of a building.

Return air

Air circulating back to the furnace or central air con­ditioning unit from the house, to be heated or cooled and sup­plied back to the living area.

Return plenum

Used in reference to mobile home furnaces: Part of the belly return system where air is drawn back to the furnace through a louver in the floor of the furnace closet.

Revolutions per minute

Number of times the crankshaft of an engine, or the shaft of a motor, rotates in one minute. RPM is a function of the design of the equipment and the power supply.

Reweatherized unit

Any unit that received weatherization ser­vices prior to September 30, 1994 and has received additional services under subsequent grants or allowed by current DOE regulations.

Ridge venting

Ridge venting is a continuous vent (or two strips of vents) along the roof ridge. Usually combined with continu­ous soffit or eave vents as part of an overall attic ventilation sys­tem.

Rim joist

The outermost joist around the perimeter of the floor framing. Also known as band joist.


Transition piece that connects the main duct to the floor and is often vulnerable to failure. See also duct boot.

Rodent barrier

Guard used to keep rodents from entering a mobile home through the belly.

Roof jack

Chimney assembly that penetrates the roof and includes the flashing and chimney cap assemblies.

Roof vent

A louver or small dome mounted on a roof (often near the ridge) to allow the passage of air through the attic.

Room air conditioner

An air conditioning unit installed through a wall or window, which cools the room by removing heat and releasing it outdoors.

Room heater

A heater located within a room and used to heat that room.

Rough opening

The framed opening in a wall into which a door or window is installed.

Safety glass

Glass that is toughened or laminated so that it is less likely to splinter when broken.


A movable or stationary part of a window that frames a piece of glass.


Describing vapor and liquid at the phase-change point. The condition in which the air cannot hold any more moisture, as a function of temperature and vapor pressure.

Savings-to-investment ratio (SIR)

SIR is computed over the life­times of the retrofit measures installed and expressed in terms of the net present value of the retail cost of the dwelling's fuel. SIRs of greater than one are counted as cost effective under this DOE WAP method of determining cost-effectiveness.


Dissolved minerals that precipitate inside boilers and stor­age tanks.

Sealed combustion

A heater that draws air for combustion from outdoors and has a sealed exhaust system.

Sealed combustion heater

A heater that draws air for combus­tion from outdoors and has a sealed exhaust system. Also called a direct-vent appliance.

Seasonal efficiency

Refers to the overall efficiency of the central heating system including on and off cycle fuel utilization and heat loss. The calculation of these factors is represented in the Annual Fuel Utilization Efficiency (AFUE) rating for the appli­ance. Distribution system loss is not factored into the AFUE.

Seasonal energy efficiency ratio (SEER)

A measurement of energy efficiency for central air conditioners. The SEER is com­puted by dividing cooling capacity, measured in BTUh, by the Watts (see also Energy Efficiency Rating).

Seasonal heating performance factor (SHPF)

Ratio of useful heat output of a heat pump to the electricity input, averaged over a heating season.

Secondary air

Combustion air surrounding a flame.

Sensible heat

The heat required to change the temperature of a material.


A bimetal switch that turns on the elements of an electric furnace in sequence.

Service equipment

The electric meter and main switch, usually located outside the building.

Service wires

The wires coming from the utility transformer to the service equipment of the building.


The heat absorbed or evolved by a substance during a change of temperature that is not accompanied by a change of state.

Shading coefficient (SC)

A decimal describing how much solar energy is transmitted through a window opening compared to clear single glass having an SC of 1.0. For example, reflective glass has an SC of 0.20 to 0.45.


Structural sheeting, attached on top of the framing, underneath the siding and roofing of a building. Any building material used for covering a building surface.

Sheet Metal and Air Conditioning Contractors' National Associa­tion (SMACNA)

An international association of contractors who specialize in heating, ventilation and air conditioning.


Common term for any building material used for cov­ering a building surface.


See drywall.


The building's exterior envelope including walls, floor, and roof.


A modular roofing material, usually asphalt, that is installed in overlapping rows to cover the entire roof.

Short circuit

A dangerous malfunction in an electrical circuit where electricity is flowing through conductors and into the ground without going through an electric load, like a light or motor.

Side jamb

Grooves in window that allow the window sashes to slide up and down or side to side.


The bottom of a window or door frame.

Sill Box

The outer area of the floor bound by the rim joist, floor joist, sill plate, and floor.

Sill Pan

A flashing device that sits on a rough-framed window sill to prevent water infiltration should water infiltrate the clad­ding and sealant around the finished window.

Single-family (SF) home

A free-standing residential building


See savings-to-investment ratio.


A non-structural screening built around the exterior of an open crawl space to exclude animals, wind and sunlight. Also has aesthetic value.

Slab-on-grade foundation

Housing base that uses concrete slabs formed from molds set in the ground. Concrete is poured into the mold all at one time, with no space left between the ground and the home.

Slider window

A slider window is essentially a double-hung window turned on its side so the sashes move horizontally.

Sling psychrometer

A device holding two thermometers that is slung through the air to measure relative humidity.


The roof section of an attic with the roof and ceiling sur­faces attached to the rafters.

Smoke-developed index

The level of smoke that a material pro­duces when burning in a fire test compared to red oak, which has a rating of 100.

Smoke tester

Device to test the amount of smoke being pro­duced by an oil burning furnace. High smoke means the fuel-to-air ratio is off, and combustion is less efficient than it should be.


The underside of a roof overhang or a small lowered ceil­ing, as above cabinets or a bathtub.

Solar absorption

Solar absorption is that portion of total solar energy neither transmitted nor reflected.

Solar exposure

The amount of solar energy falling on a horizon­tal surface.

Solar control film

Plastic films, coated with a metallic reflective surface, that are adhered to window glass to reflect solar heat gain. See also window film.

Solar gain

Heat from the sun that is absorbed by a building's materials and contributes to the heating and cooling require­ments of the dwelling.

Solar heat

Radiant energy from the sun with wavelengths between 0.7 and 1 micrometers.

Solar Heat Gain Coefficient (SHGC)

The ratio of solar heat gain through a window to incident solar heat, including both trans­mitted heat and absorbed/radiated heat.

Solar Heat Gain Factor (SHGF)

Solar heat gain amount on a surface with a particular angle and orientation expressed in Btus per square foot per hour.

Solar reflectance

The ratio of reflected to incident light. See also albedo.

Solar Screen

A framed screen designed to absorb solar heat before it transmits through window glass that is installed on the window’s exterior.

Solar transmittance

The percent of total solar energy transmit­ted by a material.

Solar water heater

System in which water is heated by solar radiation.


A magnetic device that moves a switch or valve stem.

Sone level

An international unit used to measure sound levels. One Sone is equivalent to the sound of a quiet refrigerator in a quiet kitchen.

Space conditioning

Heating, cooling, or ventilation of an indoor space.

Space heating

Heating the living spaces of the home with a room heater or central heating system.


White, chalk-like coating on concrete caused by water picking up salts as it migrates through concrete, then leaving the salts on the surface when it evaporates. Also spelled, “spalling.”


Horizontal distance between supports.

Specific heat

The ratio of the heat storage capacity of a particu­lar material to the heat storage capacity of water.


Temporary flow of combustion gases from a dilution device.


A strip of vinyl, rubber, or plastic that, when inserted into a groove, holds a screen or plastic film in place on a frame.

Split-system air conditioner

An air conditioner having the con­denser and compressor outdoors and the evaporator indoors.

Spray foam

Liquid-applied foam that expands forming a rigid foam material with millions of insulating cells.

Spot source ventilation

Spot source ventilation includes things like kitchen exhaust fans and bathroom exhaust fans.

Stack Effect

The term describes the effect of higher pressure at the top of a structure, lower pressure at the bottom of a struc­ture, and neutral pressure somewhere in between, relative to the ambient (surrounding) air pressure. It is usually the result of dif­ferent densities of warmer and cooler air (convective airflow).

Standard Work Specifications

Voluntary guidelines for quality work for residential energy upgrades. These specifications define the minimum requirements for high-quality installation of energy efficiency measures.

Standing Loss

Heat loss from a hot water storage tank through its shell.

State point

Air at a particular temperature and humidity occu­pies a single point on the psychrometric chart called a state point.

Static pressure

Measurement of pressure in a fluid filled cham­ber at a specific location. Use of a static pressure probe allows measuring pressures in forced air duct systems without regard to pressure changes due to movement of air in the system.

Steady state efficiency (SSE)

The measurement of heating effi­ciency measured by a combustion analyzer.

Steel chassis

Supporting frame for the mobile home structure exclusive of the body or housing.

Steam trap

An automatic valve that closes to trap steam in a radiator until it condenses.

Steam vent

A bimetal-operated air vent that allows air to leave steam piping and radiators, but closes when steam strikes the surface.


Full-length vertical framing members of a door.


A thin, trim board for windows and doors to close against or slide against.


Similar to furring. A nailer applied to a building sur­face.

Strike plate

The metal plate attached to the door jamb that the latch inserts into upon closing.

Strip heat

Heat provided by an electric-resistance heating cable or element as in a heat pump for auxiliary heat or emergency heat.


Plaster applied to the building's exterior walls.


A vertical wood or metal framing member used to build a wall.


The sheathing over the floor joists and under the floor covering.


The number of degrees Fahrenheit that a condenser and nearby piping cools the liquid refrigerant below its satura­tion temperature.


A person or agency that is awarded a sub-grant and is accountable to the grantee for the utilization of resources.


A layer of material to which another layer is applied.

Sulfur dioxide (SO2)

A colorless, nonflammable, water-soluble gas.

Sump pump

A pump that removes water from underneath a house or building.


The number of degrees Fahrenheit that an evapora­tor and nearby piping heats gaseous refrigerant above its satura­tion temperature.

Supply air

Air that has been heated or cooled and is moved through the ducts and to the supply registers of a home.

Suspended ceiling

Modular ceiling panels supported by a hang­ing frame.

Tankless water heater

Rather than storing hot water, a tankless unit heats water as it is being used.

Task lighting

Lighting provided at the area where a visual task is performed.


A measure of the heat present.

Temperature and pressure relief valve

A safety component required on a boiler and water heater, designed to relieve excess pressure buildup in the tank.

Temperature rise

The number of degrees of temperature that the heating fluid increases as it moves through the heat exchanger.


A unit of energy equal to 100,000 Btus or 29.3 kilowatt-hours.

Thermal barrier

A material that protects materials behind it from reaching 250° F during a fire. Drywall is a 15-minute ther­mal barrier.

Thermal break

A relatively low heat/cold conductive material separating two highly conductive materials, installed to reduce heat flow through the assembly.

Thermal bridging

Rapid heat conduction resulting from direct contact between very thermally conductive materials like metal and glass.

Thermal boundary

A line or plane where insulation and air bar­rier(s) exist in order to resist thermal transmission and air leak­age through or within a building shell.

Thermal Bypass

A large air leak that carries allows air to flow around insulation.

Thermal Conductance

A material’s ability to conduct heat, which uses the letter k.

Thermal emittance

The ability of a material to release absorbed heat.

Thermal enclosure/envelope

The boundaries of a dwelling that surround the conditioned space.

Thermal mass

A solid or liquid material that will absorb and store warmth and coolness until it is needed.

Thermal resistance

 R-value; a measurement expressing the ability to resist heat flow.

Thermal transmittance

Expressed as U-factor, thermal trans­mittance is heat flow by conduction, convection, and radiation through a non-uniform layered building component like a wall.


An electronic resistor used to sense temperature.


A bimetal-junction electric generator used to keep the safety valve of an automatic gas valve open.


The science of heat.


A device used to control a heating or cooling sys­tem to maintain a set temperature.


The raised part of a floor underneath a door that acts as an air and dust seal.

Total solar energy rejected

The percent of incident solar energy rejected by a glazing system equals solar reflectance plus the part of solar absorption that is reradiated outward.

Tracer gas

A harmless gas used to measure air leakage in a building.

Training and technical assistance (T&TA)

Program structure that ensures that all work in the field meets State standards. This ensures that there is a feedback loop and accountability within the program.


A double coil of wire that increases or decreases voltage from a primary circuit to a secondary circuit.


Decorative wood that covers cracks around window and door openings and at the corners where walls meet floors and ceilings. Sometimes called molding.


A braced framework usually in the shape of a triangle to form and support a roof.

Tuck-under garage

Architectural style in which the garage is sit­uated underneath a room of the house.

Turbine vent

Vent usually mounted on the roof of a building. The vent has at its head a globular, vaned rotor that is rotated by wind, conveying air through a duct to and from a chamber below.

Two-part foam

A triple-expanding foam appropriate for larger and more numerous air leaks, and for insulating crawl space walls and other big jobs. Two-part foam comes in portable two-tank kits and truck-mounted rigs.

Type IC Recessed Electrical Fixture

An electrical fixture that is rated to be in direct contact with fibrous insulation.

Type-S fuses

Fuse type with a rejection base that prevents tam­pering as well as mismatching.


The total heat transmission in BTUs per square feet per hour per degree Fahrenheit between the indoor and the out­doors.

U.S. Department of Agriculture (USDA)

United States govern­ment agency responsible for agricultural programs, USDA also administers some low-income housing programs.

U.S. Department of Energy (DOE)

United States government agency whose mission is to advance energy technology and pro­mote related innovation in the United States.

U.S. Department of Housing and Urban Development (HUD)

United States government agency charged with rule-making and enforcement of the HUD Code.

U.S. Environmental Protection Agency (EPA)

The mission of the U.S. Environmental Protection Agency is to protect human health and the environment.


See U-factor. An older term for U-factor.

Ultraviolet Radiation

Light radiation having wavelengths beyond the violet end of the visible spectrum; high frequency light waves.

Unconditioned Crawl Space

A crawl space without a supply of heat from a forced-air register or other heat emitter.

Unconditioned space

An area within the building envelope not intentionally heated.


Sheeting installed to provide a smooth, sound base for a finish material.


A burner that isn’t receiving a sufficient flow rate of fuel.

Underwriter's Laboratory (UL)

A private laboratory that tests materials and lists their fire-resistance characteristics.

Uniform Mechanical Code (UMC)

A model code developed by the International Association of Plumbing and Mechanical Offi­cials to govern the installation and inspection of mechanical sys­tems.

Uniform Plumbing Code (UPC)

A model code developed by the International Association of Plumbing and Mechanical Officials to govern the installation and inspection of plumbing systems.

Unintentionally conditioned

A space that is heated or cooled by energy that escapes the heating or cooling system. For example: a cooled attic or heated crawl space, which have no intentional energy delivery or comfort needs.

Unvented attic

An attic space without intentional vents to venti­late it.


An automatic vent, between the conditioned space and the attic, that operates by the pressure created by an evaporative cooler and exhausts room air into the attic. Used when open windows are a security problem.

Upflow furnace

A furnace in which the heated air flows upward as it leaves the furnace.


Toward the source of the flow.

Vapor barrier

A material that controls water-vapor diffusion to less than 0.1 perms.

Vapor diffusion

The flow of water vapor through a solid mate­rial.

Vapor permeable

A material with a water vapor permeance or more than 10 perms.

Vapor pressure

The ratio of the water vapor in an air mass to a pound of that air. Measured in grains per pound or pounds per pound. Also known as absolute humidity.

Vapor retarder

A material that controls water-vapor diffusion to less than 10 perms.


To change from a liquid to a gas.

Vaulted attic/ceiling

An attic bounded by a sloped ceiling and sloped roof, which is created by a truss and typically has more than 16 inches of space between the ceiling and roof.

Veiling reflection

Light reflection from an object or task that obscures details.


The outer layer of a building component that protects or beautifies the component.

Vent connector

The vent pipe carrying combustion gases from the appliance to a vent or chimney.

Vent chute

A lightweight plate that directs air from a soffit over attic insulation and along the bottom of the roof deck to venti­late the attic and cool the roof deck. A baffle.

Vent damper

An automatic damper powered by heat or electric­ity that closes the chimney while a heating device is off.

Vent pipe

The pipe carrying combustion gases from the appli­ance to the chimney.

Vent terminations

Where a vent leaves the building. Vent termi­nations must prevent intrusion of moisture, detritus, or pests into the building, and allow safe exhaust of vented gases.

Vented crawl space

Crawlspace with grilles or vents installed to allow for passive ventilation beneath the home.


The removal of combustion gases by a chimney or hor­izontal vent.

Venting system

A continuous passageway from a combustion appliance to the outdoors through which combustion gases can safety pass.


Refers to the controlled air exchange within a struc­ture such as local ventilation, whole-house ventilation, attic ven­tilation, and crawl space ventilation.


A heat-expanded mineral used for insulation.

Visible Transmittance

The percent of visible light transmitted by a glass assembly.


Polyethylene film vapor barrier.


The amount of electromotive force required to push a cur­rent of one ampere through a resistance of one ohm.

Voltage drop

The loss of voltage in a circuit caused by resistance.


The amount of space occupied by a three-dimensional object or region of space, expressed in cubic units.

Water-resistive barrier

Used to prevent water from contacting a building's sheathing and structural components.

Watt (W)

A unit of measure of electric power at a point in time, as capacity or demand. One Watt of power maintained over time is equal to one joule per second.


One Watt of power extended for one hour. One thousandth of a kilowatt-hour.

Watt meter

An instrument for measuring, in watts, the electric power in a circuit.


The process of reducing energy consumption and increasing comfort in buildings by improving the energy efficiency of the building while maintaining health and safety.

Weatherization Assistance Program (WAP)

DOE's Weatheriza­tion

Weatherization program notices (WPN)

Guidance documents issued by the U.S. Department of Energy for the weatherization program.

Weather-resistant barrier

See water-resistive barrier.


Flexible gaskets, often mounted in rigid metal strips, for limiting air leakage at openings in the shell like doors and windows.


A reinforcing fabric used with mastics and coatings to prevent patches from cracking.

Weep holes

Holes drilled for the purpose of allowing water to drain out of an area in a building where it has accumulated.

Wet-bulb temperature

The temperature of a dampened ther­mometer of a Sling Psychrometer used to determine relative humidity, dew point, and enthalpy.

Wet spray

Fibrous insulation mixed with water and sometimes also a binder during installation.

Whole-house fan

A fan that draws fresh outside air into the liv­ing space, flushes hot air up the attic and exhausts it to the out­side.

Whole-house ventilation

Controlled air exchange using one or more fans and duct systems.

Wind effect

House pressure and airflow between indoor and outdoors caused by the wind.

Wind washing

Air entering and leaving the attic is frequently able to blow through fibrous attic insulation, removing heat as it goes.

Window films

Plastic films coated with a metallic reflective sur­face that are adhered to window glass to reflect infrared rays from the sun.

Window frame

The sides, top, and sill of the window forming a box around window sashes and other components.

Window stop

A wood trim member nailed to the window frame to hold, position, or separate window parts. The stop is often molded into the jamb liners on sliding windows.

With reference to (WRT)

Compared to another measurement. In weatherization, a way to assess pressure differences between ducts and the rest of the home.

Work order

An order authorizing specific work to be done. Sometimes called the work scope.

Workforce Guidelines

DOE guidance on specific energy conser­vation measures; also called Standardized Work Specifications.

Work scope

The summary of energy conservation measures, materials lists and labor estimates that is prepared by an energy auditor as part of an energy audit.

Worst-case depressurization test

A safety test, performed by spe­cific procedures, designed to evaluate the probability of chim­ney back-drafting.


A room or portion of a building separated from other rooms by an air barrier.

Zone pressure diagnostics (ZPD)

Using a blower door to deter­mine the interconnectivity of various building components, which helps the practitioner locate the air barrier and know if the insulation and air barrier are aligned. Also called zonal pres­sure diagnostics.