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AlanWD
Bathroom exhaust fan vents into attic
AlanWD

I have bathroom exhaust fans that vent into the attic space. In cold temperatures when the fans are not running, the cold air drops into the bathroom through the flexible vent. The attic has gable end vents and roof vents and provides good air movement. There is no indication of mold or mildew. Any suggestions for stopping the air flow back through the flexible vent? Would a louvered dryer vent cover be a simple fix?

MLB Construction
Re: Bathroom exhaust fan vents into attic
MLB Construction

#1, install an exterior vent with a flap so that it's not venting into the attic anymore. it's not to code and you will eventually have a mold issue. you can install either one that vents through the roof or through the gable end. These exterior vent kits have a flap to prevent air flowing back into the bathroom.

#2, you can also install an inline damper to prevent air backflow.

#3, your fan should have a damper installed in it, right where the connection to the flexible duct is. maybe it broke or fell off.

A. Spruce
Re: Bathroom exhaust fan vents into attic
A. Spruce

Another vote to get it vented to the exterior with an exhaust hood that has a damper in it. It would also be a good idea to put a low spot in the vent tube for condensation to collect, rather than having it run back to and drip out of the exhaust fan.

The unfortunate thing is, even with the dampers it's still going to feel like a draft is coming back out of the fan/vent. This is partly because the dampers do not seal tight, so a certain amount of air will backdraft when the fan is not in use. The other part is that cold moves towards heat, the bathroom being warmer than the attic, you're going to notice what feels like a draft from the vent, which is actually heat transfer.

dj1
Re: Bathroom exhaust fan vents into attic
dj1

Having a well ventilated attic, as you said in your posting, is not an excuse to stop a bathroom vent at the attic. It must be vented to the outside

The above recommendations are spot on.

Mastercarpentry
Re: Bathroom exhaust fan vents into attic
Mastercarpentry

The dampers in these are never much of a seal so you're going to get some backflow and heat loss without a flap-covered external vent cap. Not a huge issue but it's there. And it must vent outside- no exceptions.

Phil

67drake
Re: Bathroom exhaust fan vents into attic
67drake

Argh....Did my roof last summer and I had to replace ALL decking due to it being rotted/soft. I found both my upstairs bathrooms vented into the attic. With my wife and I,along with 7 kids living here,we were pumping a crap ton of moisture into our attic every time we showered and turned the fan on. I vented the 2 fans to the outside,as suggested above. It might cost you a premature tear off someday,as it did in my case.

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