Duct Exhaust Fan In Attic

Bathroom exhaust fan duct length specifications.

Duct exhaust fan in attic.

Fan is vented into the attic. The bathroom exhaust ventilation fan disperses air through an opening in the fan housing which is usually 3 inches in diameter and ideally faces in the direction of the ventilation system outlet. Venting the kitchen vent fan must exhaust directly to the outside not into an attic crawlspace or a space between floors. If you have access to the attic the fan can vent either through a gable wall or roof.

Bathroom exhaust fans perform an important function by removing excess moisture from your home. The best exhaust fan venting is through smooth rigid ducts with taped joints and screwed to a special vent hood. Duct already wrapped in insulation at home centers. The warm air will exhaust out the duct and enter back into the attic through the soffit vent or ridge vent.

Moist air will condense on framing and sheathing forming ice or water that will support rot and mold or damage the rooms below. Avoid venting through a soffit vent or ridge vent. An external thermostat mounted in the attic controls the temperature and kicks the fan on when the temperature raises to the set limit. In order for attic exhaust fan to be effective you need a supply of fresh air coming in from soffits under the roof s overhang or gable vents.

You can find 4 in. Consider this a wake up call and extend the duct to vent the air outside before major damage occurs. A bath vent fan duct that is too short may violate the manufacturer s installation instructions may not work properly or may be drafty. The exhaust duct should be connected to the fan box with mechanical fasteners metal tape and or mastic and not regular cloth backed duct tape.

Terminating the duct in the attic is surprisingly common and harmful. A bath vent fan duct that is too long may restrict air flow such that the fan is not functional. Options for venting a bathroom exhaust fan include best to worst. Although this isn t always possible in attic crawl spaces you should always insulate the duct to prevent condensation problems.

Letting the fan exhaust into an open attic will cause moisture buildup on the underside of the roof. Here we provide specifications for recommended minimum maximum duct lengths for bathroom vent fans.