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 Minimum toilet vent size?
Author: LesP (WA)

Reading through the comments on this great forum, I see over and over that UPC requires a 2" vent for toilets. But combing through my code reference books, I can't find any specific reference to this requirement. The only thing I find is a table showing that a 1-1/2" vent pipe can support up to 8 DFUs (while 2" can handle 24 DFUs). Also, the vent must be 1/2 the size of the drain served.

In my renovation, I am limited by a 2"x4" wet wall, so that 1/2" makes a big difference when drilling studs. The two toilets will be draining into a 3" line which eventually meets up with the 4" building sewer. So, can I use 1-1/2" vents per code?

Thanks for your guidance -- this venting stuff is making me nuts!

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 Re: Minimum toilet vent size?
Author: North Carolina Plumber (NC)

Here in NC , we use UPC with NC amendments, if a dry vent is serving one toilet only it can be 1 1/2". If you're catching a lavatory and or bathtub with it, and 99% of the time we are, then it has to be 2".

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 Re: Minimum toilet vent size?
Author: steve (CA)

I don't have it in front of me right now, but there's a footnote at the bottom of the DFU sizing chart of the UPC, that states toilets can't use the 1½" DFU rating(ie 2" minimum).

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 Re: Minimum toilet vent size?
Author: packy (MA)

my code doesn't allow 1 1/2 for a toilet vent but i believe it would work just fine..
if we vent a toilet with 2 inch and you drain a tub into it (classic wet vent) and let a tub full of water go down the drain/vent and flush the toilet as the tub is draining, the opening in the wet went is going to be smaller than a wide open 1 1/2 pipe.

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 Re: Minimum toilet vent size?
Author: m & m (MD)

If 1 1/2" is not going to pass muster, install 2- 1 1/2" vents thru the studs and then join them together into 2" where you can.



Edited 1 times.

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 Re: Minimum toilet vent size?
Author: LesP (WA)

I am getting this work inspected, so I'll have to follow the UPC rules to a tee. There will be a lav upstream of the two toilets, so how about if I upsize the lav drain to 2" so it can serve as a wet vent?

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 Re: Minimum toilet vent size?
Author: packy (MA)

can you provide us with a rough sketch of your plan of attack?
if properly located a single 2 inch wet vent will be fine..
put a cleanout tee in the 2 inch as well...

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 Thanks for responding Packy :grin:
Author: LesP (WA)

Thanks for responding Packy.

Les



Edited 2 times.

Post Reply

 Re: Minimum toilet vent size?
Author: packy (MA)

neither link will open..
bottom of page shows how to post a picture.

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 Re: Minimum toilet vent size?
Author: LesP (WA)

Sorry Packy.

I'll try to create a PhotoBucket account later today, if that still doesn't work.

Many thanks,
Les



Edited 1 times.

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 Re: Minimum toilet vent size?
Author: LesP (WA)

Okay, here's the proposed rough-in:

[@#$%&[s1070.photobucket.com]][/URL]

And this is the layout for the two bathrooms:

[@#$%&[s1070.photobucket.com]][/URL]

Thanks again for your input!

Post Reply

 Re: Minimum toilet vent size?
Author: LesP (WA)

So, I have been noodling this some more and I see two options (although I'm sure there are many more!):

1) Wet vent the two toilets as shown which allows me to join the main drain horizontally with a tee-wye right off the toilet trap

2) Use a low heel 90 so that each toilet has a dedicated vent, but then I have to enter the drain vertically, adding another 90 degree turn after the trap

Seems like the former would be easier for draining while the latter is better for venting. So what do you pros recommend?

Thanks for your insights!
Les

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