Hello Mr. Carter:
I purchased a ranch type home built on a crawl space. It has two full baths and I have just discovered that the exhaust fans in both baths vent into the attic. Information from your excellent website tells me this is not good. I would like to know if I can vent one of these exhausts to the bathroom drain vent which is close by. This plumbing vent pipe is sealed, and vents out the roof. If this is OK? I can run an exhaust hose about 12 ft horizontally along the attic floor out to the siding for the other fan. Is this a good idea and will the exhaust fan push the hot moist air this far?
Thanking you in advance,
Patty Dee
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Patty Dee,
Absolutely positively NO! You must not cut into the plumbing vent line. If you were to do this, toxic methane gas could filter back into your bathroom through the exhaust fan ducting.
It is best to duct these fans out through the roof. Nutone/Broan make inexpensive roof cap flashings exactly for this purpose. I dislike flexible ducting intensely and would only use solid smooth galvanized metal duct pipe. The fan should be able to handle a 12 foot run with ease. Be sure to insulate the metal pipe if you live in a cold climate. This minimizes condensation formation within the exhaust pipe.
Tim Carter
www.askthebuilder.com
W3ATB