Bathroom exhaust ceiling fan - old house

jpc1September 15, 2006

1950 house with no exhaust ceiling fan in the bathroom. The remodeler stated that a fan could be installed and vented into the attic. Good idea? How about the attic air getting back in during the winter?

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Bad Idea. Venting directly into the attic will cause a moisture buildup in your attic causing all kinds of problems.

For an extra $20.00 you can buy a roof vent that the exhaust attaches to a vents it outside. Do not use flex pipe on the bathroom exhaust. Use solid pipe and put an insulated slleve on it or wrap it with insulation do a straight run to the vent without very many elbows where condensation can form and pool.

Here is a link that might be useful: installing a batroom fan

    Bookmark   September 15, 2006 at 1:46PM
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I agree for the most part with the above post. However, I think the article on the provided link goes a bit overboard. It is definitely a bad idea to vent a bathroom fan into the attic. However, flexible ducting is commonly used for bathroom fans (not for dryers which should have smooth metal duct). It is also fairly common to terminate the duct by butting it up to a vent opening in the wall or roof. I have seen many installations like this and have never seen them cause mold or wood rot (the amount of humid air that would get back into the attic is minute). While it probably wouldn't hurt to insulate the duct, I've rarely seen that done, with no adverse effects.

    Bookmark   September 15, 2006 at 1:59PM
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Bathroom vents by code must be vented to the outside. You cannot terminate the vent into the attic or by butting it up to a vent opening in a wall or roof. Doing so creates not only moisture issues in the attic but also creates a fire hazard by creating an opening to the attic by which fire can travel from lower floors.

The best method is to vent vertically up into the attic then horizontally to a gable end wall. Short of that, the vent should terminate through the roof as rjoh878646 stated.

Ducts should be rigid or flexible metal only. Plastic ducts are illegal in most places because they create a fire opening between stories.

    Bookmark   September 15, 2006 at 4:43PM
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When we remodeled our (exhaust fan-less) bathroom last fall, we went with a wall exhaust fan rather than a ceiling one... we vented it right out through to the outside wall (a few feet below the fan itself). It was much easier than dealing with attic venting, and we've had no problems with it.

    Bookmark   September 17, 2006 at 8:23PM
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I've been looking for an answer to this problem... Our cookie-cutter builder installed our bath exhaust fans and terminated the venting in the attic. He used flexible ducting, but it's not insulated, and it terminates ~1/2 the way up the attic interior.

I now have wonderful water stains on my ceiling from moisture condensing in the ducting and draining back down through the fan and pooling on the fan cover.

Will replacing the ducting with an insulated duct solve my condensation problem, or will I need to get the pipe run all the way to the ridge vent (which would require me hauling a ladder into my attic, and I am less than enthusiastic about that idea) too?

    Bookmark   December 18, 2007 at 1:01PM
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you need to run the duct on out. the moisture is from teh steam of your shower, so insulation will do no good. get the proper outdoor cover for whether you are mounting to teh wall or thru the roof.

    Bookmark   December 18, 2007 at 2:21PM
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