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Thread: bathroom vent fan

  1. #1
    DIY Junior Member pcm's Avatar
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    Default bathroom vent fan

    Hello, newb here.

    We are on the finishing end of remodeling our bathroom. It measures 7x7 with an 8 foot ceiling. The fan we bought is 70 CFM.

    Is this going to be enough to vent the bathroom adequately? Another question we have is how long can we run the vent line?

    Thank you, pcm

  2. #2
    Plumber jimbo's Avatar
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    "By the book", that is enough. I like to get a larger and quieter fan. Makes a lot of difference. I recommend about 100 CFM and max. 1.0 sones.

  3. #3
    DIY Junior Member pcm's Avatar
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    Thank you for the advise. I will go for the 100CFM. We have another bathroom in the basement that is smaller and used very little. Maybe that will be a nice place for the 70CFM.

  4. #4
    DIY Junior Member pcm's Avatar
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    I traded the 70CFM for the 100. Now my next question is.

    To get to the East side of my house there will be about a 20 foot run of 4 inch pipe for the vent fan. Is this going to be to much?

    I could go the the West and be looking at maybe 4 feet but I am somewhat bothered about the dominate Northwest winds. I need to exit out through the soffit.
    Thanks, pcm the novice DIYer

  5. #5
    Retired Defense Industry Engineer jadnashua's Avatar
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    The instructions will indicate the maximum run the fan can support. Keep in mind that with a run that long, you'll likely condense most of the moisture from the hot humid air. You need to ensure you use solid ductwork (not the corregated plastic crap) and slope it, or it will drip back into the room. It's much better to go through the roof, or run it in the joist bay and run it out the sidewall rather than the soffit.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  6. #6
    DIY Junior Member pcm's Avatar
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    Thank you, I will follow the joist bay and exit the sidewall. Hopefully 3 more short days and we will have this bathroom finished.

    If I had known about all the little unforeseen things to fix or change I think we would have waited on it.

    Thanks again.
    Thanks, pcm the novice DIYer

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