How-To Videos

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):

  1. Through the roof or an exterior gable wall.
  2. Behind a gable vent.
  3. 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.

Further Information

Print   Video Transcript

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.


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10 Comments on “How to Properly Vent a Bathroom Exhaust Fan in an Attic”

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  • Ken Says:
    October 31st, 2017 at 8:00 am

    Can I tie it into my gas water heater vent. That already passes through the roof and I’m thinking it will save another hole in roof. I was thinking of an in-line backflow preventer just to keep any carbon monoxide from back feeding if that would happen.



  • RICHARD I MARUBAYASHI Says:
    October 8th, 2017 at 2:59 pm

    I want to go with option 2, exhausting through my existing gable vent, but I cannot find a fitting that will easily mount behind the vent. I think I’m going to have to improvise with a wall vent. Don’t they make a simple fitting for this purpose?



  • Joe Says:
    July 10th, 2017 at 8:10 am

    Are we sure it’s okay to put it behind the gable vent? Mine was vented directly into the attic, so I ran 4″ duct and butted it up against the gable vent. I did this based on your article and for some reason it has me a bit worried. Can you show some pictures of this being done properly? Thanks



  • Earl S Handy Says:
    May 9th, 2017 at 3:42 pm

    I don’t like the idea of putting holes in the roof so I routed mine through the exterior wall like a dryer vent



  • Pat Thompson Says:
    January 12th, 2017 at 10:37 am

    My home is like Betty’s. The master bathroom and the 2nd bathroom vent through the roof and through the same opening. The 2nd bathroom vent drips on the floor and is ruining the ceiling. The 2 pipes, one a 4″ (master) and the other a 3″ (2nd) do not go through the ceiling but into a common box that goes through the roof. The house is too high to see if that box has any kind of fitting on the roof but it doesn’t look like it from the attic. None of the pipes are insulated and neither is the box they go into. The master bath pipe is about 30′ long and the 2nd bath pipe is about 10′ long. Thank you for this forum. Pat Thompson



  • Betty Marchione Says:
    November 27th, 2016 at 11:40 am

    My bathroom exhaust fan drips water down on the toilet and floor and also the ceiling is wet around it. It vents into the attic. How can I fix this?



  • Alex Says:
    November 19th, 2016 at 7:05 am

    How do I connected the vent pipe at the roof?



  • m. scanlon Says:
    November 15th, 2016 at 5:09 pm

    I ALSO! AM INTERESTED IN MOUNTING A UNIVERSAL TV AERIAL IN THE ATTIC FOR PUBLIC ACCESS STATIONS. COULD YOU SUPPLY THE INFO
    AND MAKE A RECOMMENDATION RE THE BEST ANTENNA. WE LIVE
    MANY MILES(possibly 50) mi) FROM NEAREST BROADCASTER.
    THANK YOU
    M. SCANLON


  • Official Comment:


    Lindsay Hughes Says:
    May 3rd, 2016 at 2:16 pm

    Nic, in our “Household Innovations” episode, we installed a Channel Master CM3020 antenna with Channel Master TITAN 2 CM-7777 Antenna Preamplifier in the attic and oriented it in the direction of the TV stations. You can watch the full episode here: http://www.todayshomeowner.com/video/energy-efficient-household-innovations/



  • NIC MANOCHEO Says:
    May 2nd, 2016 at 2:53 pm

    ON A RECENT TV SHOW, YOU DEMONSTRATED HOW TO MOUNT A UNIVERSAL TV AERIAL IN AN ATTIC TO BRING IN PUBLIC ACCESS STATIONS. HOW CAN I GET MORE INFO ON THIS MATTER. THANK YOU


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How to Properly Vent a Bathroom Exhaust Fan in an Attic