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  1. #1

    bathroom exhaust vent - how many feet

    We're finishing our walk-out basement and have a bathroom at one end of the house (underground part). We need to vent the exhaust fan to the other end (walk-out part). The bathroom was roughed-in by the builder so they put it in that area.

    The problem is that my contractor says the length of the vent is too long. He thought he remembered 25 feet is the maximum length for a bathroom bent and you have to take off 2.5 feet for each 90 degree bend. The length from the bathroom to outside is about 28 feet and we will have one 90 degree bend. I asked him to show me the code but he hasn't gotten back to me.

    The builder put the bathroom there so I'm assuming they knew the codes. Going through to the roof would be about the same length. BTW it's a 4 inch vent. Any ideas?

  2. #2
    Join Date
    Jun 2008
    Can't say I've ever heard of that, but that doesn't mean much. I've got one that I think is a little more than 25'. Pretty sure it has no 90 bends.

    Why not call your town code enforcement office yourself? They should be able to tell you, provide a rationale if it is truly code, and maybe a workaround.

  3. #3
    Join Date
    Jan 2004
    I think he's thinking of a dryer vent.

    Call your local code agency, thsy will know.
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  4. #4
    Thanks, while searching for more answers, I came across an engineering site that states:

    "Section R303.3 of the 2000 IRC states that all bathrooms and toilet rooms must have an operable window or a mechanical venting system. If a mechanical system is used, it must discharge to the outside. If the vent pipe runs more than 15 feet the fan will not be able to discharge the air.The problem comes in when we have bathrooms located in the inner part of the dwelling. It may require a special roof jack above this bathroom to be in full compliance."

    Now this is saying 15 feet or less to be effective but that would depend on how good the fan is. It doesn't say anything about what the code demands.

    I'll call my county to see what they say. Thanks for the quick responses.

  5. #5
    Join Date
    Aug 2003
    Lincoln, Nebraska
    Codes here in Nebraska will let us run a bath fan as far as we need to. May have to increase to 5". I think you would be alright.

    How come your HVAC guy dosn't know the codes for your area?
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