View Full Version : Bathroom exhaust venting question

09-12-2007, 08:19 PM
This could apply to the plumbing forum as well. Since I'm remodeling the bathroom I went ahead and bought a new exhaust fan to install. The previous owners just had the exhaust venting into the attic :mad: so I will be running a new vent. Now my question, is it possible/permissible to just run pvc off the exhaust and hook into my main stack? It would hook in right below the rafters so it would be at the top of everything and the stack turns into 3" before going through the roof. I am just trying to avoid cutting anymore holes in walls. My other option would be to run a duct about 13' to the closest gable end wall and out through the wall, again I just am trying to avoid another hole anywhere.


09-12-2007, 08:55 PM
Your third optio would be to go directly through the roof, why not do that? I just did my first 4 roof vent-caps, and it's not to hard

09-12-2007, 09:18 PM
Brand new roof. Openings in the roof are the biggest cause of leaks. That's my last resort, the family has a large roofing business so it's not that I can't do it, I just know the headaches that come with chasing roof leaks. That and I don't want to look at another pipe coming through the roof.

09-12-2007, 09:37 PM
I hope that I didn't cause major headaches by installing roof vents, I was told that if a roof vent was installed properly it should be fine. I'm new to installing roof vents, are there any specific problems/methods I should be aware of?

Also; I understand your aesthetic concern, I'm only concerned about running the moist hot air for too long of a run.

09-12-2007, 10:08 PM
Just make sure your pipe boots are tight fitting and that they were worked into the shingles correctly (under the first row or two depending on size of boot, then on top of the last row it covers) and make sure all small nail holes in the shingles being pulled up are caulked, along with the uphill side of the boot where the shingles are cut out around it. I was worried about the 13' being too long of a run as well.

09-13-2007, 05:39 AM

You do not, under any circumstance, want to cut into your main vent stack for your bathroom fan. That would expose your house to sewage gas, a major code violation, and health issue.

09-13-2007, 07:51 AM
I am surprised it was about 5 replies down the line before someone got in with the answer: DO NOT UNDER ANY CIRCUMSTANCES tie an exhaust into a plumbing vent. The emphasis in my reply should eliminate the need for long winded explanations why.

As far as going through the roof, that is something to be careful about, but it is done all the time. You could also run it to a sidewall, or even to a soffit, although the latter can lead to problems of moisture right near that soffit location.

09-13-2007, 09:11 AM
Understood on the "not tying into stack" part. Is the 13ft. too long of a stretch to run it to the end gable?

09-13-2007, 12:22 PM
Generically, no, 13' would work. Specifically, hard to tell. Each brand and model will come with specifications on the maximum distance and the number of elbows it will support. the instructions are often available on line prior to purchase so you can figure it out.