# Proper use of DWV fittings for venting



## CBP (Feb 5, 2010)

This is a question mostly for Illinois guys, but curious about practices in other areas as well. 
I came across an installation recently where I questioned 2 vent connections in the attic. The first was a 2 x 1-1/2 x 2 san tee on it's side, with the branch going toward the vent stack and both ends of the run picking up vents from below. (See first pic). On the other, there was a 3" combo directly below the VTR. The inlet of the run was bushed down to 2", again picking up vents from below. (See 2nd pic).
Am I wrong in thinking that these fittings are installed incorrectly?? If the 2" on the run on the tee and the 3" outlet of the combo are pitched down, then the inlets of these are pitched up (even if the pipe is flexed enough to pitch down). He said it was common practice. His argument was that any water in the vents still drains back to the waste stack. 
Thoughts?


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## breplum (Mar 21, 2009)

According to the UPC, a twin ell is the only proper fitting to function in both cases. 
Of course everything will still function the way it is...


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## CBP (Feb 5, 2010)

I was thinking a san tee with a street ell. (never was a fan of twin ells)


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## The Dane (Feb 19, 2015)

We use UPC and we do venting like that except the Wye and 45 going through roof would probably have been a 90 then a San tee on the side to pick up the vent on the left and then followed by a 90 to go to the vent on the right. UPC states that Venting must be sloped down back towards the drain

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## plumb1801 (Apr 4, 2014)

In my area san tee's can be use on their back or sides in any dry venting situation. I will often use a san tee on its back where an individual vent is required as long as no waste is discharging through it (vertical to horizontal). The fittings are cheaper and I believe it allows the air to escape easier with less restriction. Of this is only my opinion no scientific studies to support this theory.


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## CBP (Feb 5, 2010)

I agree that san tees can be used for dry venting. The question is with the direction of flow in the fitting. I have always taught, been taught and installed them so that the outlet of the run of the tee or wye should be towards the VTR, not the branch of the wye or tee. This just seems like lazy plumbing to me.


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## GAN (Jul 10, 2012)

Being in Illinois, technically this is a code violation. You could use a twin ell, but if you look that fitting up in our Illinois code book, it is not listed either. I have not found an inspector that would call a twin ell. You may get a called on a sanitary tee.

Will it work yes, you can also say it is restricting the flow of air. That may be countered by using a 2" tee with a 2" x 1 1/2" bushing, by oversizing the affect on air restriction would be less (not that it makes that much difference anyway).

Standing the tee up and using a street ell in the heel and bringing the other into the branch would be an approved method. As far as trapping condensation as long as both the heel and run drain back it wont be an issue. What you don't want to do is have a reducing coupling in a horizontal position. That will trap condensation. You can roll the pipe down and put a reducing coupling on the 45 degree roll then flatten back out again to the smaller piping without trapping water. Comes in handy when you exceed the 20% horizontal rule.


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