Bathroom Exhaust Fan Venting

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Chris Wagner

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Hello,

Im remodeling our kids second floor 5x8 bathroom. We need to replace the fan. I went up in the attic and the current fan has a 3" duct running to the soffit, it just lays there. No vent cap . The plywood under the roof has just light traces of dust/lint. No mold,black spots etc. The duct length is 4ft .

I will need to replace ducting to 4" for new fan. Is it ok to run the new ducting the same route to soffit and add a vent cap with damper ?

Thanks!
 

Jadnashua

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Personally, I don't like running that hot, moist air into a soffit. Especially if you live where it is cold in the winter. THat excess damp air can just end up inside your roof from the soffit vents, likely right near. But, take a close look at the paint and wood around that area...if it's in good shape, it's probably the easiest thing to do and won't result in anything. GIven a chance, I'd much rather route it out a gable end or up through the roof than out a soffit. There are distance and elbow distances that have to be abided by with the exhaust on any fan...the longer you have to run it, the bigger the pipe that is required. Most vent caps are not designed to be mounted upside down and will not seal.
 

Chris Wagner

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Smooky-Thanks for the links

Jim- I read about this when running my new dryer ducting and soffit was a big no for that. However the bathroom fan is 21ft away from Gable and would hate to have to cut into my 4 month old roof. These are the builders fans that were put in 21 years ago. I could only get so close to see without getting stuck in the back with roofing nails. But I just could see dust, lint. No piles or anything like that. The roof was just of 4 months ago and they checked for any rot, stains,etc. I could get the extension out and look up from the outisde
 

Jadnashua

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If the moisture has not damaged anything in the time you have had it in, a new one probably won't be an issue, either. Look for bubbles in the paint, or spongy wood. You may need an in-line check valve and an outlet with a screen on it rather than the more common flapper valve in it so that it would close. My original vent was just dumped into the attic...a really lousy way to do it. My choice was either do that again, or out the roof (in a row of townhouses - Gambrel roof, so roof either horizontally or vertically, chose vertically - hot air pumps better that way!). Pay careful attention to the total length, size, and installed elbows to make sure that you are not impacting the fan's operation. The Panasonic unit I put into my mother's house would accept either 4 or 6" duct, and because of the distance I had to run it, required the 6" ducting.
 
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