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Thread: Maximum length of duct for bathroom fan

  1. #1
    DIY Junior Member Douche's Avatar
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    Apr 2006
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    Default Maximum length of duct for bathroom fan

    I have a small bathroom (less than 80 sq feet). I am installing an exhaust fan on the ceiling in my upstairs bathroom. I prefer to vent the duct out the attic wall rather than the roof. The wall is approximately 15 feet from the location of the exhaust fan. My question is there a maximum duct work distance or is there a certain cfm fan or fan speed I need to blow open the vent at 15 feet? I plan on using flexible metal duct.

    Thanks!

  2. #2
    Plumber jimbo's Avatar
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    Aug 2004
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    There is no regulation on this. 15 feet is not excessive. Based on 6 air changes per hour, a 70 CFM fan would be "adequate". I always prefer to use 100 or 110 CFM even for a small room like your. This will minimize any problems with mold and mildew. Spend the extra $$$ and get a unit with a maximum sone rating of 1.0 You will live with the noise of this fan for many years, so it is worth a few bucks to go quiet.

  3. #3
    DIY Junior Member Douche's Avatar
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    Apr 2006
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    Many thanks..appreciate the advice!!!

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