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Old 12-06-2011, 09:02 AM   #1
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Venting a new bathroom exhaust fan


Hi all,

I'm putting in a new exhaust fan in my bathroom...there has never been one and since I've got the ceiling out, this looks like a good time to remedy the problem. I'm looking to vent through the roof.

I've looked around at lowes for roof vents, but can't find one that looks like it will work. The manufacturer says to use a dryer type vent with backflow preventer.

I have a 4" outlet on the fan...and was wondering if flex tubing would work. I have very limited space with the pitch of the roof and subroof sheathing.

Any help will be appreciated.

Thanks, Ed

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Old 12-06-2011, 09:36 AM   #2
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Venting a new bathroom exhaust fan


I'm sure somewhere there's the correct roof vent, but I wouldn't vent through the roof at all. Any condensation in the vent tubing will run back down into the bathroom when you shut off the fan. Every bathroom vent I've ever seen went through the wall or soffit.

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Old 12-06-2011, 10:35 AM   #3
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Venting a new bathroom exhaust fan


If you can vent through the wall or soffit, that's great. But you have to be extremely careful in cold climates to not put a bathroom vent underneath a vented soffit. The air will rise up into your roofing system, and water condense on your roofing plywood and make your insulation wet/less efficient. Worst of all, the wet plywood insulation are great places for mold to grow. I've heard many stories of folks who have had to replace parts of their roof after 5 years due to this very issue. If you live in a climate where frost/snow occur - don't vent a bathroom fan under vented soffit... it's not a great idea in warm climates either.

If you need to do a roof vent - these are the type that typically get used - often called roof caps - hoods, etc. They work great for shingle roofs.

http://www.homedepot.com/buy/bath/ba...kit-66750.html
http://www.lowes.com/ProductDisplay?...=207236-14-636

The "kit" from home depot is probably a bad idea in a cold climate - you'll need insulated ducting to prevent condensation from forming and running back down through your fan.

If you have a metal roof, you'll need to adapt to a pipe that extends through your roof with a cap on top of that (Pipe is sealed with a rubber boot on a metal roof)
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Old 12-06-2011, 03:27 PM   #4
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Venting a new bathroom exhaust fan


I don't really have the option to run my vent to the soffit...if I did, that's what I'd do...since I'm right next to an outside wall.

I don't really want to put an ugly vent on the front wall of my home...so, that's out.

Therefore, it leaves the roof. I've been looking at the Broan kit and using insulated 4" flex pipe...so it won't sweat.

I'm right next to the roof...not the best place to be...where should I put the vent...how far from the ridge...half way down...just wondering.

Last edited by Ed911; 12-07-2011 at 05:44 AM.
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Old 12-06-2011, 06:19 PM   #5
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Venting a new bathroom exhaust fan


Those roof vents are sold right next to the fans for the bathroom. The pipe needs to be a short as possiple and no 90's also. Location on the roof does not really matter, if your in a snow area the top 4' is best because the snow melts there first.
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Old 12-06-2011, 06:51 PM   #6
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Venting a new bathroom exhaust fan


Quote:
Originally Posted by joecaption View Post
Those roof vents are sold right next to the fans for the bathroom. The pipe needs to be a short as possible and no 90's also. Location on the roof does not really matter, if your in a snow area the top 4' is best because the snow melts there first.
I guess that I should have looked there...the guy at Lowe's took me to the back of the store and showed me a Broan attic vent...or so I'm thinking now...hmmm...

I guess that's what I get for expecting the big box store to have knowledgeable help.

It's good to be able to bounce issues off of the forum members here...much appreciated.

Since I'm not a real capenter...just a pretend one...I have to think things through...sometimes for a while.

Thanks, Ed
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Old 12-06-2011, 07:50 PM   #7
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Venting a new bathroom exhaust fan


I just had the same issue, the guy at Home Depot that claimed to be a roofing expert had zero clue where the cap was sold.

As was stated it's in a box on a shelf right next to the fans. I used their cap and bought the 4 inch insulated duct individually.

I went through the roof with mine, no problems as of yet.
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Old 12-07-2011, 06:04 AM   #8
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Venting a new bathroom exhaust fan


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Originally Posted by oldhouseguy View Post
I just had the same issue, the guy at Home Depot that claimed to be a roofing expert had zero clue where the cap was sold.

As was stated it's in a box on a shelf right next to the fans. I used their cap and bought the 4 inch insulated duct individually.

I went through the roof with mine, no problems as of yet.
Yep, looks like the deal. I decided to add the vent fan now...while I have the ceiling out, because the way that my house is built, the main roof line rafters tie in right above my master bath and they are sheathed...so, the only access to the bathroom ceiling is from a cutout that is between two rafters about 8 feet away. A lot of crawling and wiggling, if I don't do it now.

I have one other question about this exhaust fan installation. The fan that I bought can move 110 CFM, but my bathroom is like airtight when the door is closed...so, I'm wondering if that won't hinder the fans ability to exhaust the humidity out of the room. I was wondering if I should undercut the door...but, that doesn't sound right. Any suggestions, or comments?

Last edited by Ed911; 12-14-2011 at 09:20 AM.
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Old 12-14-2011, 09:22 AM   #9
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Venting a new bathroom exhaust fan


Quote:
Originally Posted by oldhouseguy View Post
I just had the same issue, the guy at Home Depot that claimed to be a roofing expert had zero clue where the cap was sold.

As was stated it's in a box on a shelf right next to the fans. I used their cap and bought the 4 inch insulated duct individually.

I went through the roof with mine, no problems as of yet.
Thanks for the guidance...found one. It's sure a lot smaller than the one he showed me.

Question...what is the best roofing adhesive for the install...is one that much better than the other?

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