Chapter 12: Air Leakage Diagnostics
This chapter focuses on pressure-testing homes, to determine their airtightness and to guide air-sealing during weatherization. Ideally the air barrier and insulation are aligned. The airtightness of the air barrier has a substantial effect on comfort, energy efficiency, and performance of the insulation. The testing described here helps to analyze the existing air barriers and decide whether and where air-sealing is needed.
12.1 Shell Air-Leakage Fundamentals
Controlling shell air leakage is a key concern for successful weatherization. The decisions you make about sealing air leaks affect a building throughout its lifespan. Air leakage has these impacts.
• Air leakage accounts for a significant percentage of a building’s heat loss.
• Air leakage through insulated assemblies reduces the R-value of insulation.
• Air leakage moves moisture in and out of the house, wetting and/or drying the building.
• Air leakage causes house pressures that can interfere with the venting of combustion appliances.
• Air leakage causes comfort problems for occupants which can impact their control of the heating and cooling equipment.
Air Leakage and Ventilation
Most homes depend on air leakage to provide outdoor air for diluting pollutants and admitting fresh air. However, air leaks can also bring pollutants into the home. Mechanical ventilation is a more reliable and efficient way to provide fresh air. See ASHRAE Standard 62.2–2016 Ventilation.
12.1.1 Goals of Air-Leakage Testing
Air-leakage testing accomplishes a variety of purposes.
• Air-leakage and pressure testing measures the home’s air-tightness level.
• It evaluates the home’s ventilation requirements.
• It helps you to decide how much time and effort is required to achieve cost-effective air-leakage and duct-leakage reductions.
• It helps to compare the air-tightness of the air barriers on either side of an intermediate zone, such as an attic or crawl space. For example, comparing the airtightness of the plaster ceiling with that of the ventilated sloped roof gives the auditor an idea of how leaky the ceiling is.
• It helps decide the best place to establish the air barrier in an area that has no obvious thermal boundary such as an uninsulated crawl space.
The reason for the complexity of air-leakage testing is that there is so much uncertainty about air leakage. Testing is needed because there simply is no accurate prescriptive method for determining the severity and location of leaks, especially in complex homes. Depending on the complexity of a home, you may need to perform varying levels of testing to evaluate shell air leakage. In particular, the number of major components like stories, additions, corners, and gables indicates a home’s potential for large air-leakage reductions.
Air-Sealing with Air-Leakage Testing
Dedicate most of your effort to seal the large air leaks that pass directly through the thermal boundary. Chasing small leaks or leaks that connect to the outdoors through interior walls or floors isn’t worth as much effort.
✓ Perform blower door testing.
✓ Determine the test results to find if air sealing is cost-effective.
✓ Prioritize air leaks: ducts, attic, garage, major low level leaks.
✓ Locate and seal the air leaks.
✓ During air-sealing, monitor your progress with blower door testing. Smoke can be used to test areas sealed.
✓ Stop air sealing when air-sealing goals have been achieved or the budget limit has been reached.
12.2 Single-Family Airtightness Testing
House airtightness testing was made possible by the development of the blower door. The blower door measures a home’s leakage rate at a standard pressure of 50 pascals. This leakage measurement can be used to compare homes with one another and to established air-leakage standards.
The blower door also allows the auditor to test parts of the home’s air barrier to locate air leaks. Sometimes air leaks are obvious. More often, the leaks are hidden, and you need to find their location. This section outlines the basics of blower door measurement along with some techniques for gathering clues about the location of air leaks.
The blower door creates a 50-pascal pressure difference across the building shell and measures airflow in cubic feet per minute (CFM50), in order to measure the leakiness of homes. The blower door also creates pressure differences between the interior living spaces in the house and intermediate zones like attics and crawl spaces. These pressure differences can give clues about the location and combined size of a home’s hidden air leaks.
Connecting the digital manometer’s hoses correctly is essential for accurate testing.
This method uses the phrase with-reference-to (WRT), to distinguish between the input zone and reference zone for a particular measurement. The outdoors is the most commonly used reference zone for blower door testing. The reference zone is considered to be the zero point on the pressure scale.
For example, house WRT outdoors = –50 pascals means that the house (input) is 50 pascals negative compared to the outdoors (reference or zero-point). This pressure reading is called the house pressure.
Low-Flow Rings
During the blower door test, the manometer measures pressure and calculates airflow through the fan. This airflow (CFM50) is the primary measurement of a home’s airtightness and is directly proportional to the size of the home’s air leaks. For the blower door to measure airflow accurately, the air must be flowing at an adequate speed. Tighter buildings and smaller buildings don’t have enough air leakage to create an adequate airspeed to create the minimum fan pressure. This low-flow condition requires using one or two low-flow rings, to reduce the blower-door fan’s opening and to increase air speed, fan pressure, and measurement accuracy.
When the air speed is too low, the DG-700 displays “LO” in the Channel B display. After installing one of the low-flow rings, follow the manufacturer’s instructions for selecting the proper range or configuration on the digital manometer.
12.2.2 Preparing for a Blower Door Test
Preparing the house for a blower door test involves putting the house in its normal heating-season operation with all conditioned zones open to the blower door. Try to anticipate safety problems that the blower door test could cause, particularly with combustion appliances.
• Identify the location of the thermal boundary and determine which house zones are conditioned.
• Identify large air leaks that could prevent the blower door from achieving adequate pressure, such as a pet-door.
• Put the house into its heating-season operation with windows, doors, and vents closed and air registers open.
• Turn off combustion appliances temporarily.
• Open interior doors so that all indoor areas inside the thermal boundary are connected to the blower door. This could include the basement, conditioned kneewall areas, and closets.
Avoiding Risky Situations
Don’t perform a blower door test in risky situations like the following until you remove the risk or perform an acceptable building repair.
• A wood stove is burning.
• Holes in the ceiling that could lead to dust pollution during a blower door test.
• Extremely weak building components, like a poorly installed suspended ceiling or loose wood wall paneling.
• Lead, vermiculite, or asbestos dust is present.
• Potential sewer gas.
• Waste in the basement or crawl space.
12.2.3 Blower-Door Test Procedures
Follow this general procedure when performing a blower-door test.
✓ Set up the house for winter conditions with exterior doors, primary windows and storm windows closed. The door to the basement should be either open or closed, according to whether or not the basement is considered to be within the thermal boundary.
✓ Install blower door frame, panel, and fan in an exterior doorway with a clear path to outdoors. On windy days, install the blower door on the home’s leeward side if possible. Pay attention to the blower door’s location and any other conditions that may affect test results.
✓ Follow manufacturer’s instructions for fan orientation and digital-manometer setup for either pressurization or depressurization. Depressurization is the most common orientation.
✓ Connect Channel A of the digital manometer to measure house WRT outdoors. Place the outside hose at least 5 feet away from the fan.
✓ Connect Channel B to measure fan WRT zone near fan inlet. Do not place the hose directly in front of the fan intake.
✓ Ensure that children, pets, and other potential interferences are at a safe distance from the fan.
Conducting the Blower Door Test
Follow these instructions for performing a blower door test, when using a DG700 digital manometer. For other blower door and digital manometer models, please refer to the manufacturer’s instructions.
1. Turn on the manometer by pushing the ON/OFF button.
2. Select the MODE: PR/FL@50.
3. Select the correct DEVICE that matches the blower door you’re using.
4. With the fan covered, conduct the BASELINE procedure to cancel out the background wind and stack pressures. Let the manometer average the baseline pressure for at least 30 seconds.
5. Remove the cover from the blower door fan. Complete the next two steps for tighter buildings.
6. Install the flow ring in the blower door fan which matches the expected flow rate. The fan pressure should be at least 25 Pa while measuring CFM@50.
7. Push CONFIG or Range button until you match the flow ring being used.
8. Turn on the blower door fan slowly with the controller. Increase fan speed until the building depressurization on the Channel A screen is between –45 and –55 pascals. It doesn’t need to be exactly –50 pascals.
9. The Channel B screen will display the single-point CFM50 air leakage of the building. If this number is fluctuating a lot, push the TIME AVG button to increase the averaging time period.
10. You can also use the cruise-control function to automatically control the fan speed to create and hold –50 pascals of pressure.
Blower-Door Test Follow-Up
Be sure to return the house to its original condition.
✓ Inspect combustion appliance pilot lights to ensure that blower door testing didn’t extinguish them.
✓ Reset thermostats of heaters and water heaters that were turned down for testing.
✓ Remove any temporary plugs that were installed to increase house pressure.
✓ Document the location where the blower door was installed.
✓ Document any unusual conditions affecting the blower door test.
12.2.4 Approximate Leakage Area
There are several ways to convert blower-door CFM50 measurements into square inches of total leakage area. A simple and rough way to convert CFM50 into an approximate leakage area (ALA) is to divide CFM50 by 10. The ALA can help you visualize the size of openings you’re looking for in a home or section of a home.
12.2.5 Multifamily Air Leakage
Energy auditors develop an air sealing strategy by evaluating the chase leakage, according to the presence and location of the following building components.
• Direct air leakage through roofs, walls, and foundations.
• Vertical chases; including stairs and elevators
• Leaks through floors allowing airflow from one floor to another.
See the following sections for more information on multifamily air leakage.
• Air-Sealing Attics and Roofs
• Air Sealing Foundations and Floors
12.2.6 Multifamily Blower-Door-Test Strategies
Here we discuss three different strategies for blower-door testing a multifamily building: the whole-building test, the compartmental test, and the guarded test.
Testers also measure zonal pressures to evaluate air barriers in multifamily buildings, like they do in single-family dwellings.
Whole-Building Test
Although increasingly difficult as buildings get larger, the whole-building blower door test is a preferred approach. The testers usually need multiple blower doors for this test along with an automated blower-door-testing system.
The whole-building test provides an air-leakage measurement for the entire building. Also, this blower-door test gives the best information about where the critical leaks to outdoors are located.
Compartmental Test
The compartmental test requires only one blower door. This test measures air leakage to both the outdoors and indoors.
The compartmental approach gives the energy auditor a sample of the air leaks in a single dwelling unit. The leaks in this single unit may inform the auditor about typical leaks in all dwelling units or in units with the same characteristics.
Guarded Test
Testers use the guarded test when they want to measure a single dwelling unit’s air leakage to outdoors. This test is another strategy to characterize a single unit—like the compartmental test—by only measuring leakage to outdoors. This test requires pressurizing surrounding dwelling units with the same pressure applied to the tested unit.
Zonal Pressures
Creating and measuring zonal pressures is one of the most effective ways to evaluate air leakage in multifamily buildings. Testers observe the building’s assemblies and architectural features and formulate assumptions and questions to guide their air-leakage testing and air sealing.
The testers may decide to isolate various zones and assemblies to determine their individual leakage to outdoors or to adjacent zones. The goal is a testing and air-sealing process that is cost-effective. The tests may be quantitative or qualitative. Here are some zones and assemblies that you may want to pressure-test.
• Stairwells and elevator shafts.
• Ventilation and HVAC ducts, duct joints, and duct chases.
• Overhangs and balconies.
• Basements, crawl spaces, and penthouses.
• Floor and ceiling cavities.
The next section, Testing Air Barriers, gives many examples of zone pressure testing.
Leaks in air barriers cause energy and moisture problems in many homes. Air-barrier leak-testing avoids unnecessary visual inspection and unnecessary air sealing in hard-to-reach areas.
Advanced pressure tests measure pressure differences between zones in order to estimate air leakage between zones. Use these tests to make decisions about where to direct your air-sealing efforts, for example.
• Evaluate the airtightness of portions of a building’s air barrier, especially floors and ceilings.
• Decide which of two possible air barriers to air seal — for example, the floor versus foundation walls.
• Determine whether building cavities like porch roofs, floor cavities, and overhangs are conduits for air leakage.
• Determine whether building cavities, intermediate zones, and ducts are connected together through air leaks.
• Estimate the air leakage in CFM50 through a particular air barrier, for the purpose of estimating the effort and cost necessary to seal the leaks.
Air-Barrier Test Results
Air-barrier tests provide a range of information from simple clues about which parts of a building leak the most, to specific estimates of the airflow and hole size through a particular air barrier.
The next table shows examples of how common building materials perform as air barriers. This information is helpful in interpreting blower door tests and selecting air-sealing materials.
12.3.1 Primary Versus Secondary Air Barriers
A home’s air barrier should be a material that is continuous, sealed at the seams, and impermeable to airflow. Where there are two possible air barriers, in an attic for example, the most airtight pressure boundary is the primary air barrier and the least airtight is the secondary air barrier.
The primary air barrier should be adjacent to the insulation to ensure the insulation’s effectiveness. We use zone pressure diagnostics testing to verify that the insulation and the primary air barrier are together. Sometimes we’re surprised during testing to find that our assumed primary air barrier is actually secondary, and the secondary air barrier is primary.
Intermediate zones are unconditioned spaces that are sheltered within the exterior shell of the house. Intermediate zones can be located inside or outside the home’s primary air barrier. Intermediate zones include: unheated basements, crawl spaces, attics, enclosed porches, and attached garages.
Intermediate zones have two potential air barriers: one between the zone and house and one between the zone and outdoors. For example, an attic or roof space has two air barriers: the ceiling and roof. You should know which air barrier is the tightest.
Blower door tests give us valuable information about the relative leakiness of rooms or sections of the home. Listed below are five simple methods.
1. Feeling zone air leakage: Close an interior door partially so that there is a one-inch gap between the door and door jamb. Feel the airflow along the length of that crack, and compare that airflow intensity with airflow from other rooms, using this same technique.
2. Observing the ceiling/attic floor: Pressurize the home and observe the top-floor ceiling from the attic with a good flashlight. Air leaks will show in movement of loose-fill insulation, blowing dust, moving cobwebs, etc.
3. Observing smoke movement: Pressurize the home and observe the movement of tracer smoke through the house and out of its air leaks. You can also use a small piece of tissue paper to disclose air movement.
4. Room pressure difference: Check the pressure difference between a closed room or zone and the main body of a home. Larger pressure differences indicate larger potential air leakage within the closed room or else a tight air barrier between the room and main body. A small pressure difference means little leakage to the outdoors through the room or a leaky air barrier between the house and room.
5. Room airflow difference: Measure the house CFM50 with all interior doors open. Close the door to a single room, and note the difference in the CFM50 reading. The difference is the approximate leakage through that room’s air barrier.
Tests 1, 2, and 3 present good client education opportunities. Feeling airflow or observing smoke are simple observations, but have helped identify many air leaks that could otherwise have remained hidden.
When airflow within the home is restricted by closing a door, as in tests 4 and 5, it may take alternative indoor paths that render these tests somewhat misleading. Only practice and experience can guide your decisions about the applicability and usefulness of these general indicators.
12.3.3 Zone Pressure Diagnostics
ZPD can be used to determine many important air sealing metrics.
• If air sealing has been effective.
• If a thermal boundary is aligned with an air barrier or boundary.
• The square inches of leakage from the house to an attic or a house to an attached garage.
• If a moldy crawl space is connected to the living area above.
12.3.4 Advanced Zone Pressure Diagnostics
The use of the REDCalc software will simplify the process of testing intermediate zones and providing accurate estimates of leakage between the house and zone. The following are the basic steps necessary to conduct the test.
1. Follow the blower door guidance found in Preparing for a Blower Door Testand Blower-Door Test Proceduresto assure the house is set up for winter conditions.
2. Depressurize the house to -50 Pa and record the CFM50 measurement.
3. While the house is at -50 Pa, measure the pressure difference between the target zone and the outside/inside.
a. It is usually best to measure the zone with reference to outside. Accuracy is higher when pressure differences are measured across the “loosest” surface which is usually the zone to the outside for attics and garages but may be the zone to the inside when measuring basement leakage.
4. Turn off the blower door.
5. Open a hole between the zone and outside or zone and inside.
a. You should open the hole on the side of the zone that is the “tightest” surface which will show the highest pressure drop and there must be 10 Pa change or greater when the hole is added to assure accurate readings. The tightest surface opening is often between the zone and house. (e.g. the door from the house to garage or the attic hatch.) However, the tightest surface may be between the zone and the outside. E.G the bulkhead door for basement zone leakage measurements.
6. Depressurize the building to -50 Pa and record the CFM50 measurement.
7. While the house is at -50 Pa, measure the pressure difference between the target zone and the outside/inside.
a. Take this measurement with reference to the same place as you did earlier.
8. Enter the data into the REDCalc tool http://www.residentialenergydynamics.com/REDCalcFree/Tools/ZonePressureDiagnostics and calculate the leakage between the building and zone, zone to outside and the total path. Be careful to select the proper location of the added hole.
The accuracy of your measurements can be improved by taking baseline pressures as you would with blower door tests. This is more important for attic measurements since the stack effect can impact the results when measuring attic leakage. Here’s how to do this prior to running the blower door:
• Use a separate manometer to measure pressure differences. Run a hose from the left upper tap of this manometer to the zone you are measuring making sure to keep the hose end out of air flow paths created by the blower door. The lower left reference tap remains open unless you are measuring pressure difference between the zone and outside, If you are measuring pressure between the zone and outside, run a 2nd hose from the reference tap to the outside.
• Zero out any pressure difference using the baseline feature on the manometer. Proceed with the measurements outlined above.
ZPD Cautions:
• Be sure hose ends are outside of air flow paths when taking pressure measurements. For example, measuring attic pressures across a closed attic hatch with lots of air leakage and a pressure probe barely entering the attic could significantly affect the results.
• Interpreting the results can be tricky. E.G. If the attic of the garage is open to the attic of the house, the results will show the leakage between the house and combined attic/garage zones.
• High error rates indicate results that may not be considered valid.
12.3.5 Zone Pressure Diagnostics Example: Attached and Drive-under Garages
Attached or drive under garages pose a significant threat to occupant health due to the amount of carbon monoxide that can be given off by vehicles and the volatile organic compounds often stored there. Natural and mechanically induced air flow through buildings often results in the substances being “pulled” into the home. Building Performance Institute Standards 8.3, NH Energy Code, and the DOE Standard Work Specifications 6.6003.5b all call for providing an effective air barrier between attached garages and living spaces.
When an attached or drive under garage is present, an air barrier must be established between the garage and living space when weatherizing a home or else the weatherization work must be deferred. When a new wall, ceiling, or door is installed – it must meet building codes. This usually means using fire rated doors and 5/8” drywall. The garage ceiling and/or wall should be air sealed before applying insulation and the fire rated surface material. The newly applied surface should then also be air sealed. For example, if a drywall ceiling is being applied to a drive under garage area, penetrations such as electrical and plumbing should first be sealed. The ceiling can then be insulated with batts or blown in insulation and the drywall installed. The ceiling should then be taped along with a coat of drywall mud. All edges should be sealed. Any plugs installed with blown in insulation should also be sealed.
A visual evaluation along with a running blower door and smoke to guide air sealing of the interface and to confirm the living space is adequately separated from the garage must be completed.
Quantifiable zonal pressure diagnostics (ZPD) should be used as an aid in verifying the effectiveness of the air sealing when practical. Software such as RED Calc ZPD can quantify the CFM50 air leakage between the garage and house. The ZPD garage to house leakage goal is 200 CFM50 or less.
The air leakage status between the house and garage must be documented in the client file. A comparison between starting and ending airtightness should be part of the documentation.
A carbon monoxide monitor with display must be installed near the entry into the living space and where air flow into the living space can be most effectively sampled by the carbon monoxide monitor. Two monitors may need to be installed in homes with attached garages to adequately monitor carbon monoxide levels.
If garage exhaust fans are installed, SWS 6.6003.5a standards must be followed.
If the work required will result in the project falling below an SIR of 1, then the project must be deferred unless non-DOE supplemental funding is available.