Circuit Venting Question

[wwhitney]

Hello,

I'm not very familiar with circuit venting, although I've done a bit of reading and have gone over the IPC code section (914). https://up.codes/viewer/colorado/ipc-2018/chapter/9/vents#914

I have a question about the interplay of 914.2 "The circuit vent connection shall be located between the two most upstream fixture drains" and 914.5 "Fixtures, other than the circuit-vented fixtures, are permitted to discharge to the horizontal branch drain."

I understand 914.5 to mean that the horizontal branch drain with the circuit vented fixtures can have other separately vented fixtures discharging into it, at any place, including upstream of all the circuit vented fixtures. So in that situation, what is the proper interpretation of "two most upstream fixture drains" in 914.2?

It could mean the "two most upstream circuit vented fixture drains," which would be clear. But it doesn't say that. It could mean the "two most upstream fixture drains of any venting type," although that would be weird if there are two or more separately vented fixture drains upstream of the circuit vented drains.

Function wise, it seems like the reason for 914.2, when there are no upstream separately vented fixture drains, is to put the vent connection at the upstream end while ensuring that the horizontal vent just downstream of the vent connection is washed by a fixture. That avoids a horizontal drain vent that could foul.

So from that point of view, "between the two most upstream fixture drains" should mean "downstream of at least one fixture drain (of any venting type), and downstream of at most one circuit vented fixture drain". Is that a reasonable interpretation?

Any thought would be appreciated.

Cheers, Wayne

 

[James Henry]

"Circuit vent" A dry vent that can vent a minimum of two fixtures and a maximum of eight fixtures, The vent must be a dry vent and the fixtures must enter the drain on the horizontal, including toilets. the vent must be located between the two upper most fixtures.

 

[Sponsor]

 

[wwhitney]

Thanks James, I agree.

Your drawing shows an individually vented fixture drain joining the horizontal drain line downstream of all 3 circuit vented fixtures. My question is what happens when the individually vented fixture drain enters the horizontal drain line upstream of all the circuit vented fixtures. The language in IPC 914.5 or UPC 911.5 allows either case.

Cheers, Wayne

 

[James Henry]

My question is what happens when the individually vented fixture drain enters the horizontal drain line upstream of all the circuit vented fixtures.

Then you would essentially have a wet vent scenario. A circuit vent is mainly used when the upper most fixtures are water closets as is common in gang bathrooms and because a toilet can't wet vent a bathroom, the only difference between a circuit vent and a wet vent is that the vent has to be a dry vent and be between the first two toilets.

 

[wwhitney]

Then you would essentially have a wet vent scenario.

Agreed it's very similar, but more flexible than a horizontal wet vent, as it's not restricted to bathroom groups. You can have unrelated, separately vented fixtures draining through the circuit vent as well.

It might be convenient in some cases like this to put the circuit dry vent connection just upstream of all the circuit vented fixtures. The horizontal circuit vent would still be washed by the upstream individually vented fixture. So I don't see any reason it wouldn't work well, and I find the code language a bit ambiguous, as I mentioned.

Cheers, Wayne