Cold Air coming in through bathroom exhaust fan

rwallen1961November 12, 2008

I just moved into a fairly new house (3 years old) and now that the weather has turned more winter-like, I'm noticing that cold air is pouring into the bathroom via the exhaust fan.

Strangely enough, there is no vent to the outside so this is clearly dumping the exhaust into the attic and while I did go up there, there is no visible fan anywhere to be found. It is in an odd spot in a corner of the roof so very little clearance in that spot.

My there some type of "flap" or something that is suppose to open when the fan is on and then close when the fan is off (much like a dryer vent)? Anyone have any ideas on how to resolve this problem?

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There's an outside chance that your duct runs between joists and dumps out your soffit. Go dig gingerly through the insulation to make sure before you incur costs.

But if there's no ducting, you need to get this dealt with as soon as possible. Warm, damp air exhausting into a cold attic condenses and can cause mold and destroy insulation, or (worst case) more serious structural rot.

The symptom you've noticed (cold air) will be fixed when someone puts a backflow damper in the complete duct system.

Seriously: if there's no ducting, fix this soon. And have a good inspection to see if any damage has occurred already.

    Bookmark   November 12, 2008 at 6:26PM
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I just had a fan installed the other day and they said it vents to the soffit - I was wondering if this would lead to cold air coming back into the bathroom but since it's only been 2 days I haven't been able to tell. Is it not a good idea to vent through the soffit? I'm sure they didn't install any back flow contraption - should I call them back and tell them we need one?

    Bookmark   November 12, 2008 at 8:46PM
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All the fans I have ever seen had backflow flappers as part of the fan housing. They weren't separate options. Maybe the flapper is binding and held open, or maybe you have a really strong exhaust somewhere else in the house that sucks air in through the bath fan. The flapper isn't an air-tight seal. It just restricts a large air flow back into the house.

    Bookmark   November 12, 2008 at 10:48PM
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jomama517, to answer your question, it's okay to vent through the soffit. If you feel lots of cold air through a system that has ducting, it's usually a stuck damper as noted above.

    Bookmark   November 13, 2008 at 5:54AM
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OK...problem is now resolved (I think). I managed to get the cover and light fixture out of the unit, then removed the fan assembly to see if I could see things better.

There is a contra-flow "flap" that was stuck in an open position. I could close by pushing it shut with a screwdriver, but then when I opened it again, it stayed open. Perhaps some lint build-up or something like that, but anyway, there was a plastic tab that is to act as a counter-balance to make the thing shut again so I attached a small paper clip type thing to it to give it just an extra bit of weight.

Now when I push it open with a screwdriver, it opens and then closes back on it's own.

As for the venting piece, I really can't see if it's venting directly into the soffit, but I suspect you are right. It is so far back into a corner of the house, it's virtually impossible to see.

Thanks to all for your help and advice. I love this kind of teamwork.

    Bookmark   November 13, 2008 at 11:23AM
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... I'm still begging you to go into the attic and make sure you have ducting... There was a well-publicized case of a house that had to be demolished a few years ago because the ducting hadn't been done. The kicker was that *all* the parts were sitting up in the attic, waiting to be installed.

    Bookmark   November 13, 2008 at 3:11PM
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