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Community and Q&A

Poor options for bathroom venting

SouthDakotaRoof | Posted in General Questions on

My recently bought home has a history of ice dams (climate zone 6a) I’m working of fixing that in all the usual ways. One thing has me stumped though. My tiny bathroom is on a exterior wall and my ceiling mounted bathroom fan was venting into the attic. I need a new venting route. I have read roof venting not advised because of snow and soffit venting not advised because of moisture.

I could do gable wall venting but there are a few issues.
-the gable wall is facing into the wind. Our blizzards and heavy winds usually slam in from the west.
-It would be an 11′ long run. I’ve read that long runs are to be avoided.
-The straight shot would put the vent right above a window. I’d have to add more length and turns to avoid window.
-Height of fan box & ceiling joist means the duct would be perfect level to run over joists so I dont know how to create a downward slope to it.
Or instead I could buy a wall mounted vent. But that would be pretty close to the soffit and then we are talking moisture in the soffit again. And I’ve read they can they’re not so good in snow country because of condensation dripping and thermal bridging.

What is the sensible way?

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  1. user-2310254 | | #1


    It sounds like you already may have read this article by Michael Maines. But in case that is not the case...

  2. Expert Member
    AKOS TOTH | | #2


    The best is gable vent. If you get a decent wall cap, wind should not be an issue. Look for ones that have a foam gasket as they tend to seal better.

    11' run is not long. You have to make sure that if you use flex duct it doesn't sag and create ares where water can pool. What you need to do is run the duct first up, than slowly slope it down towards the gable wall. You can hang the duct from your rafters, don't need to run it across the floor. Make sure the duct is insulated all the way to the gable end.

    Vent above a window is not an issue.

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