Duct Exhaust Fan In Attic

Here we provide specifications for recommended minimum maximum duct lengths for bathroom vent fans.

Duct exhaust fan in attic. Letting the fan exhaust into an open attic will cause moisture buildup on the underside of the roof. Terminating the duct in the attic is surprisingly common and harmful. Bathroom exhaust fan duct length specifications. You can find 4 in.

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. Although this isn t always possible in attic crawl spaces you should always insulate the duct to prevent condensation problems. If you have access to the attic the fan can vent either through a gable wall or roof. A bath vent fan duct that is too short may violate the manufacturer s installation instructions may not work properly or may be drafty.

Consider this a wake up call and extend the duct to vent the air outside before major damage occurs. An external thermostat mounted in the attic controls the temperature and kicks the fan on when the temperature raises to the set limit. The warm air will exhaust out the duct and enter back into the attic through the soffit vent or ridge vent. When venting a bathroom exhaust fan make sure to vent the air to the outside rather than into your attic where it can cause mold and mildew to form.

Avoid venting through a soffit vent or ridge vent. Options for venting a bathroom exhaust fan include best to worst. A bath vent fan duct that is too long may restrict air flow such that the fan is not functional. 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. Duct already wrapped in insulation at home centers. Moist air will condense on framing and sheathing forming ice or water that will support rot and mold or damage the rooms below. A 3 or 4 inch duct connects to the outlet on the fan housing and runs to a side wall or to the roof and connects to a vent cap that allows the.

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. The best exhaust fan venting is through smooth rigid ducts with taped joints and screwed to a special vent hood.