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  • bath fan

    I have a small bathroom, 9x5. fan is close to middle of room. Its new and I believe it is 80cfm. It is vented into the soffit with dryer vent hose. There is also a window in bathroom. My problem is when you take a shower the whole bathroom steams up so bad the walls are dripping wet, the blinds are rusting and water drips from the fan. All of this with the door open! Found hose was kinked so does a little better but not good enough. What should I do? Vent to roof, bigger fan?

  • #2
    Re: bath fan

    is this post in wrong place?

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    • #3
      Re: bath fan

      Originally posted by pesciwasp View Post
      is this post in wrong place?
      You're in the right place. There are more plumbers than builders on this site, so the responses in this section aren't as fast.
      Exactly what type of material is the hose?
      Wire ribbed plastic? Flex aluminum?
      How long is the run and how many turns does it have?
      Turn on the fan and go outside and feel for the flow of air.
      If you have access, replace the hose with solid aluminum ducting and that should help.

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      • #4
        Re: bath fan

        Check the exhaust hose run through the attic space. If it runs across the rafters and is not supported it will sag in between the rafters. These low spots will collect moisture which WILL condense and end up filling the hose and blocking it off. Then you will get ZERO flow.
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        • #5
          Re: bath fan

          If the vent is between the shower and the fresh air (bathroom door) most of the vented air will be the fresh air. The fan needs to be as far away from the fresh replacement air as possible. Make sure there is a gap under your bathroom door so that exchange air can make it into the room. With the cooler temps now all that hot moist air is likely condensing in the dryer vent pipe and dripping back into the fan. Using solid pipe as suggested is way better than that plastic flex junk. When replacing it make sure there is a straight run of about 2' before a bend sloped toward the exhaust vent so moisture is directed away form the fan. Tape all the pipe joints and elbows with aluminum tape (not duct tape) and wrap the pipe with insulation

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          • #6
            Re: bath fan

            You've got too small a fan, that's just a noise maker for moving air.


            I tell my customers to start at 130 cfm's and go up, not down.


            Don't care if the bathroom is 5' by 6', or even a 2' by 3' closet, those smaller fans just do not do a good job.


            Down always puts you in the less than $100 range which attracts the spendthrifts.
            Northern Kentucky Plumbers Twitter Feed | Plumbing Videos

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            • #7
              Re: bath fan

              Thanx for all the replies. The hose is ribbed, only bend is when reaches the soffit, no sagging, halfway between the shower door and main door, and the problem exists with the bathroom door open! I think that answers all questions. Seems to me that i need straight insulated pipe, vented through the roof, with a much more powerful fan. Thanx again.

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              • #8
                Re: bath fan

                Understand that a fan rated at 80cfm or 10,000cfm is a FACTORY rating..... reality is a different story.

                An easy test: With the bath fan on take 2-squares of 2-ply toilet paper; hold the paper up to the fan flat in the palm of your hand; if the fan sucks up and holds 1 of the squares you have LESS than 50cfm; if the fan holds both of the squares then you have ~50cfm; if the squares are sucked outta your hand, through the fan and squirt out of the soffit then you have ~100cfm.

                Weird I know but trust me - it is pretty danged accurate.

                Other factors to consider:

                *The exterior wall - is it painted or wallpaper (really hoping that it is NOT papered)?
                *Does this happen year round or only certain seasons (assuming that you always take a hot shower)?
                *What is the air flow of the vent (from the HVAC unit) if any into the bathroom?
                *How old is the house?

                One thing that may reduce the damage/irritation would be to aim a Vornado or similar-type fan into the bathroom from another room to help blend/mix the air. This is virtually moot in the winter assuming that you are heating in that season (e.g. if you are in Phoenix it's rare that you'd use heat).

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