What are the maximum lengths for running a 2" or 3" vent pipe horizontally?

I would like to merge the vents from multiple fixtures into a single roof vent.

Thanks,

Anthony

It depends on what your code says. In Illinois no more than 20 percent of the developed length can be horizontal. A way around this is to oversize the vent, by increasing 2" horizontal vent to 3" horizontal vent. you need to check with your inspector and see if he will buy off on this.

Anthony, under the UPC, 2" can run a horzontal maximum of 40' and 3" can go
70.67'. There is a note though, that says "When vents are increased 1 pipe size for their entire length, the maximum length limitations specified in this table do not apply". What will apply isn't stated.....

> Anthony, under the UPC, 2" can run a
> horizontal maximum of 40' and 3" can go
> 70.67'.

My plan was to run a main 3" horizontal vent line along the length of the house (about 40'), with the vertical vent pipe in the center. Then I was going to connect the 2" vent pipes from each fixture to the main 3" line.

The longest run would work out to about 20' of 2" vent and 20' of 3" vent.

Does this sound like an acceptable arrangement under UPC? It would be really nice to only have a single roof penetration, even though it would add a lot more pipe.

Anthony

Anthony, it sounds ok to me. Is the 3" the only vent for the house? Is the main drain exiting the house 3"?

> Anthony, it sounds ok to me. Is the 3" the only vent for the
> house? Is the main drain exiting the house 3"?

I'm looking at a couple of options.

A single 3" vent through the roof, and a 3" main drain exiting the house.

My other option is to run a 4" main line down the center of the house, with smaller 2" and 3" lines connecting to that. In that case, I would run two 3" vents to the roof.

My concern with the 4" pipe is with the low flow toilets. I've heard that they don't provide enough water to flush the 4" pipe as well as the 3" pipe. Any truth to this theory?

Also, logistically, I may have to go with the two vent option anyway. We'll have cathedral ceilings in our house, and I'm not sure yet if there will be room to get a horizontal vent up and over the peak of the ceiling to meet up with the rest of the vents.

Anthony

said by awatson "My concern with the 4" pipe is with the low flow toilets. I've heard that they don't provide enough water to flush the 4" pipe as well as the 3" pipe. Any truth to this theory?"


Yes using a pipe too large for the load on it actually does more harm that good. When water drains in a properly sized drain it creates a scouring or swirling action. Too large a pipe negates this. Also in too large of a pipe there wouldn't be enough water to carry the solids. Code where I work (South Carolina) only requires us to use 4" where you would have more than 3 toilets draining into it. i.e. if we had 5 toilets we would run 4 inch to the second toilet and reduce to 3 inch to catch the last three toilets.

> Code where I work (South Carolina) only
> requires us to use 4" where you would have
> more than 3 toilets draining into it.

Interesting, thanks for the information...

We'll only have two toilets in the house, so I may just stick with 3" pipe for the whole system, regardless of my venting choice. 3" would be cheaper and easier to route than the 4" would anyway.

Anthony

I assume when you say this, that you realize that once it clears the top of the cathedral ceiling, it cannot drop down, but has to continue rising until it meets the main vent.

> once it clears the top of the cathedral
> ceiling, it cannot drop down, but has to
> continue rising until it meets the main vent.

Understood. There will be approximately 4' of attic above the peak of the cathedral ceiling. According to the plans, this should be more than enough space to allow a horizontal vent to pass over the peak and meet up with the main vent in the rest of the house (which has a higher roof peak).

Anthony