How to Properly Vent a Bathroom Exhaust Fan in an Attic
By: Danny Lipford
Bathroom exhaust fans perform an important function by removing excess moisture from your home. 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.
Options for venting a bathroom exhaust fan include (best to worst):
- Through the roof or an exterior gable wall.
- Behind a gable vent.
- Behind a soffit vent.
To improve venting and reduce air resistance in the vent pipe:
- Keep the run of vent pipe as short and straight as possible.
- When possible use smooth metal pipe, rather than flexible ductwork.
Watch this video to find out more.
- Where and How to Install a Bathroom Vent Fan (article)
- Replacing a Bathroom Exhaust Vent Fan (video)
- How to Maintain a Bathroom Vent Fan (video)
- Bathroom Vent Fan CFM Calculator (article)
Danny Lipford: Jim asks, “Is it OK to have a bath exhaust fan vent into my attic?”
No, it’s never a good idea to have any exhaust fan in your home dump all that hot, moist air in your attic. It can cause you a lot of problems with mold and mildew forming on the underside of your rafters and decking as well as getting into your insulation.
Several different ways you can move that hot air to the outside. One is to route it over to a soffit vent and attach it to the back of the soffit vent, but this can work against your exhaust fan because that’s actually an air intake, so not as good as other methods.
Another method, a little bit better, is if you have a gable-style roof and a gable vent on one end of the house, you can attach this to the back of a gable vent.
But the absolute best way to get that hot, moist air out of your house is to route it straight up through the roof and out a roof cap on it. Even better, instead of using this flexible type pipe, use a smooth metal pipe to route it through the roof.