9.3   Fan and Duct Specifications

This section covers fan and duct specifications for both local ventilation and whole-building ventilation. Duct sizing, materi­als, and installation determine whether airflow meets the design amount (CFM). Most existing exhaust fans and ventilation sys­tems don’t achieve their design airflow because of installation flaws.

9.3.1   Fan Specifications

SWS Detail: 6.6003.1 Surface-Mounted Ducted, 6.6003.2 Inline, 6.6003.3 Through the Wall, 6.6003.4 Multi-Port System, 6.6003.5 Garage Exhaust Fan, 6.6288.1 Sound-Rating Limits

Continuous ventilation is highly recommended because it sim­plifies design and control. Continuous ventilation also mini­mizes depressurization by allowing selection of the minimum-sized fan. Exhaust fans, installed as part of weatherization work, must vent to outdoors and should include the following features.

1.      Rated for continuous operation if the fan operates con­tinuously.

2.      A weatherproof termination fitting.

3.      Unless the fan operates continuously, the fan housing or termination fitting should house a backdraft damper.

4.      Noise rating and ventilation efficacy as specified in the table.

Table 9-2:         Fan Noise Limits ASHRAE 62.2 - 2013

Fan

Noise Rating (sones)

Continuous operation

1 sone or less

Local ventilation up to 400 CFM

3 sones or less

Fan Installation

Observe these procedures when installing ventilation fans.

ü       Install the fan or ventilator as close as possible to its termi­nation.

ü       Orient the fan or ventilator housing so that the exit fittings face toward their termination fittings.

ü       Remove an integral backdraft damper if the fan operates continuously.

ü       Be careful not to inhibit the back-draft-damper operation by installing screws that interfere with the damper’s move­ment or by damaging the damper housing.

ü       Repair or replace the backdraft damper on an existing fan, if the damper doesn’t open and close freely.

ü       Install in-line fans and multi-port ventilators in remote areas such as attics and crawl spaces and connect the fans to intake grilles in rooms.

ü       Isolate in-line fans and multi-port ventilators from fram­ing to minimize noise.

ü       Measure the fan airflow to verify compliance with Stan­dard 62.2 - 2013.

ü       

Ventilation00006.jpg

9.3.2   Termination Fittings

SWS Detail: 6.6002.2 Terminations, 6.6102.2 Intakes

Termination fittings for intake and exhaust ducts must exclude pests and water. Termination fittings must comply with these specifications.

ü       Termination fitting must direct water away from its open­ing.

ü       Flash or weather-seal termination fittings.

ü       Termination fittings must have insect screens over the openings.

ü       The termination-fitting collar must be the same diameter as the exhaust or intake fitting on the fan.

PVCductFitting.jpg

 

ü       If the fan has no backdraft damper and the fan operates intermittently, install a termination fitting with a backdraft damper, to operate in the direction of airflow.

ü       Fasteners must not interfere with backdraft-damper oper­ation.

FanTermination.jpg

 

Locating Termination Fittings

Locate termination fittings using these specifications.

ü       At least 6 inches above grade

ü       At least 10 feet from another fan termination

ü       Above local snow or flood line

ü       At least18 inches above a sloped asphalt based roof

ü       Never on a flat roof

ü       As required by local building authority

ü       Exhaust terminations must be at least 3 feet away from an operable window, an exterior door, or the property line.

9.3.3   Duct Sizing

Fans often fail to deliver their rated airflow capacity. Bends, un-straight flex duct, dirty grills, and backdraft dampers can reduce design airflow by 50% or more.

If you follow the sizing in this table, you may achieve the fan’s rated airflow for short duct runs with a maximum of two elbows.

For more detailed duct-sizing recommendations, see“ASHRAE 62.2 Duct Sizing” on page 481.

Table 9-3:         Round Duct Diameters (inches) for Desired Airflows

Desired

CFM

25

50

75

100

150

200

Rigid

4

5

6

7

8

9

Flex duct

5

6

7

8

9

10

Friction rate = 0.05; maximum equivalent length =100 feet

9.3.4   Duct Materials and Installation

SWS Detail: 6.6002.1 Ducts, 6.6002.2 Terminations, 6.6003.2 Inline, 6.6003.1 Surface-Mounted Ducted, 6.6003.4 Multi-Port System, 6.6005.2 Kitchen Range, 6.6102.1 Outside Air Ventilation Supply Ducts, 6.6102.2 Intakes, 6.6103.1 Inline or Multi-Port, 6.6202.2 Heat Recovery Ventilator (HRV) and Energy Recovery Ventilator (ERV) Installation

This sections covers SWS requirements and best practices for installing ventilation ducts connected to exhaust fans, ventila­tors, and air handlers.

See also "Sealing Duct Leaks" on page 319.

Rigid Duct Installation

Observe these best practices for installing rigid ventilation ducts.

ü       Prefer rigid smooth metal pipe (30 gauge or thicker) or plastic pipe (Schedule 30 or thicker) for ventilation duct.

ü       Limit elbows to a maximum of two per duct run.

ü       Use three equally spaced sheet-metal screws to fasten sec­tions of round metal duct together.

ü       Join rigid duct sections so the edge of male end of a duct section isn’t opposing airflow.

ü       Follow manufacturer’s instructions to join other types of rigid ducts together.

ü       Seal all rigid-duct joints and seams with mastic, mastic and webbing, or metal tape, labeled UL181B or UL181B-M. See “Sealing Duct Leaks” on page 319.

ü       Support metal ducts with at least 1/2-inch, 18 gage strap­ping or at least 12-gage galvanized wire, not less than 10 feet apart.

ü       Insulate metal ducts to R-8 to prevent condensation if they travel through unconditioned spaces. See “Duct Insulation” on page 324.

ü       Fasten PVC exhaust ducts together with approved PVC cement.

Flexible Duct Installation

Observe these best practices for installing flexible ducts.

ü       Stretch flex duct and support it every 4 feet with a 1.5-inch duct support.

ü       Use tool-tensioned plastic tie bands to join both the inner liner and the outer liner of the flex duct to the rigid duct or a fitting on the fan or termination fitting.

ü       Install a screw to secure the flex duct and tie band to the metal duct between the tie band and the end of the metal duct.

ü       Flexible air duct material must meet UL 181, NFPA 90A/90B, International Mechanical Code, or the Uniform Mechanical Code.

Flx_Mtl_Jnt.jpg