# Preventing the bathroom fan from back drafting cold air



## drewdin (Jan 8, 2014)

It's pretty cold here in the northeast. I have found my bathroom to be very old in the morning, I have a window and bathroom fan that is vented through the roof. The duct take a 90 out of the fan, goes up about 5' long and out of the roof. I can feel cold air coming in if I put my hand in front of the vent. 

What type of dampers do you guys recommend to prevent cold backdrafts? I have found 50 different dampers but I don't want to put junk in. Thanks


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## bud16415 (Jan 8, 2014)

I have always just used the ones with the butterfly flapper valve that fit in the line. Do you have one that&#8217;s not working or just a straight shot?


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## Wuzzat? (Jan 8, 2014)

bud16415 said:


> I have always just used the ones with the butterfly flapper valve that fit in the line. Do you have one that&#8217;s not working or just a straight shot?


Yeah, the valve works on gravity.

Use a candle flame to tell if the cold air is actually moving in under pressure or only sinking due to the stack effect.

If a negative pressure in your house, or winds, prevent yours from working to your satisfaction you could go with a 24vac motorized damper.


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## kok328 (Jan 8, 2014)

Replace the assembly for a couple of bucks, all newer bathroom exhaust fans have the check vavle already as part of the unit.


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## nealtw (Jan 8, 2014)

They are only a flap of metal you may have one that is stuck, you should be able to find it from inside the unit on the bathroom side. It will be just outside the unit where the air exits. None will stop air flow if you have a shortage of air in the house. Other fans or furnace or people can use more air than is being supplied by fresh air vent, if you have one.


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## drewdin (Jan 10, 2014)

i found the one on the inside, i guess when they installed the new one about ayear ago it was installed at an angle. So the flap does not completely close. I was thinking about adding one to the straight section of pipe that goes through the roof. ill wait for now


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## Drywallinfo (Jan 10, 2014)

I have an inexpensive vent kit that I picked up at Menards. See http://www.menards.com/main/bath/bath-fans/broan-roof-vent-kit/p-189618-c-5869.htm  Our bathroom vent vents straight up through an attic and out and with as cold as -25F temps we had no back draft.  I think what will help a lot is to insulate this pipe. And the easiest and best way to do this is with expanding foam - just spray around the pipe with one can, let it expand and set up and spray more cans as needed. The foam will insulate and also prevent any moisture from escaping the vent pipe by sealing it up.  But you will have to wait til it is warmer. For now you could wrap the pipe with fiberglass and tape it.  See a pic of the spray foam on the vent pipe at http://www.drywallinfo.com/drywall-mold-removal.html


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## Wuzzat? (Jan 11, 2014)

^ That's what I put on one of the fan vents.  No complaints so far.


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