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venting celing bathroom fan


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Please help

We want to install a ceiling bathroom fan in our 2nd floor bathroom. The ceiling level is above the roof level, so we have to vent through the soffit or through the roof. I heard conflicting reports regarding venting through soffits. We have a nice Panasonic WhisperFit Fan, and one electrician said that venting through a soffit was no problem, since the fan comes with a damper which will reduce the backdraft. My primary concerns are moisture condensation and heat loss. We live in Wisconsin. Can we vent through the soffit? We certainly do not want to deal with mold down the road. What should i do? Thanks!

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You can vent through the soffit, but with the WI climate I'd be more inclined to recommend venting through the roof. The warm moist air wants to rise. So even though it's discharged to the outdoors below the soffit, it will want to rise towards the soffit again....especially in the winter time. If it were my house, I'd go with the vent through the roof.

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icon_speech_sigh.gifBut what about special soffit exhoust vents? I bought one this weekend that claims to let warm air out, but shuts when the fan is not blowing? Is that acceptable? Also, i have been warned about roof installations because apparently, if you do not patch the roof perfectly, it will certainly leak. The last Alternative is to run a good 15 ft long tube along the roof line in the attic, and run it to the wall at the back of the house. Then a wall vent can be used.
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Hi,

I've never seen anything but trouble with soffit venting. When properly installed a rain cap designed specifically to vent a bath fan through the plane of the roof will not leak. There is no need to "patch" the roof perfectly, because the cap flange is integrated into the roof shingles. They are even used on shake roofs around here and don't leak despite the uneven surface.

Whoever is telling you that, should go to his proctologist and get his head freed up.

ONE TEAM - ONE FIGHT!!!

Mike

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Hi,

You can do that. Except, you need to insulate the duct so air won't cool to dewpoint and condense inside, you should not use corrugated ducting and the duct needs to not have any dips in it that could end up pooling water.

You also need to be careful about what's directly overhead. I've never personally seen vents that exhaust out the side of a house cause any attic issues, but others who've posted here have posted pictures of some serious moisture-related issues involving vents that discharge outside of sidewalls beneath the eaves.

OT - OF!!!

M.

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Originally posted by weirdhellokitty

icon_speech_ok.gif What about running it along the floor of the attic to the wall at the back of the house? Is it bad to run the ducting about 15-18 feet?

Yes. Flexible ducting creates turbulent air flow; this turbulence creates static pressure, which reduces air flow. The longer the duct, the greater the static pressure. A 15-18 foot run will probably create too much static for a bath fan to effectively counteract. It will also allow moisture to condense on the interior of the duct.

Just run it through the roof; it's easy, & they don't leak if the installer has a grain of know-how. At minimum, discharge the duct within 6" of a standard roof vent; this isn't "legal", but it works fine.

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Originally posted by weirdhellokitty

However, we plan on finishing the attic to become livable space. This has been the most difficult project ever, and it seems like every option sucks. :(

Making an attic "livable space" is a very bad idea, regardless of how you vent the exhaust vents. That attic needs to be highly vented for many reasons.

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Originally posted by kurt

Other option.....

Get an inline Fantech fan going on; they have a bathroom/water closet fan that moves around 800cfm minus static. You mount the fan @ the outlet anywhere (more or less) that you want (up, down, sideways), & pull the bath air out silently. One fan can service multiple bathrooms.

http://www.fantech.net/bathroom.htm

Very cool!

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Good stuff Kurt, great tip.

Weird cat...make sure that you get plenty of ventilation (a power vent makes a lot of sense here) in the little bit of attic space (if any) you have left or in each and every rafter bay. I would definitely recommend a low intake and high exhaust whether by ridge vent or power actuated. It's gonna be hot up there.

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  • 3 years later...

Curious

M1506.2 Recirculation of air. Exhaust air from bathrooms

and toilet rooms shall not be recirculated within a residence or

to another dwelling unit and shall be exhausted directly to the

outdoors. Exhaust air from bathrooms and toilet rooms shall

not discharge into an attic, crawl space or other areas inside the

building.

Underlining and bold are mine.

IRC M1501.1 Outdoor discharge. the air removed by every mechanical exhaust system shall be discharged to the outdoors. Air shall not be exhausted into an attic, soffit, ridge vent or crawl space.

1501.1 says air shall not be exhausted into a soffit.. Does that mean a soffit or thru a soffit vent opening?

If the subject question involved a back flow damper, it seems it would be acceptable based on 1506.2. I keep hearing about icing of condensation at soffit vents - we don't have that problem here.

How come the code people keep changing the numbers?? In 2003 edition 1501.1 was for clothes dryers exhaust.

Inserted quotes are 2006.

Dammit! I just noticed this thread started over 3 years ago...Oh well.

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Doesn't the new 2006 IRC require bathroom vents (such as this) to actually vent outside and does not allow these to vent just at the soffit? In other words, instead of the vent terminating just inside the soffit, I believe the new 2006 IRC requires the vent to terminate PAST the soffit (literally now outside) to prevent mold growth on roof sheathing, etc.

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