Thread: Vent caps

Anyone know about how much air space is necessary in front of a typical waste vent or otherwise before it becomes an issue.

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Marc,

Seems to me that it would be necessary to calculate the area of the pipe opening and compare it to the area of the opening at that slot between the top of the vent pipe and the underside of the cap to see if they match. If the slot is less, then it would probably need correction.

Assuming my math is correct...

The area of an 1 1/2" pipe cross section is approximately 1.8 sq.in.
The area of a 2" pipe cross section is approximately 3.1 sq.in.

The circumference of an 1 1/2" pipe is approximately 4.7"
The circumference of a 2" pipe is approximately 6.2"

So, in order for you to get 1.8 sq.in. on a 1 1/2" pipe, you would need a gap/slot that was approximately 3/8" and about 1/2" on the 2" pipe.

If my REALLY rusty math is correct.

Originally Posted by Gunnar Alquist

Marc,

Seems to me that it would be necessary to calculate the area of the pipe opening and compare it to the area of the opening at that slot between the top of the vent pipe and the underside of the cap to see if they match. If the slot is less, then it would probably need correction.

Assuming my math is correct...

The area of an 1 1/2" pipe cross section is approximately 1.8 sq.in.
The area of a 2" pipe cross section is approximately 3.1 sq.in.

The circumference of an 1 1/2" pipe is approximately 4.7"
The circumference of a 2" pipe is approximately 6.2"

So, in order for you to get 1.8 sq.in. on a 1 1/2" pipe, you would need a gap/slot that was approximately 3/8" and about 1/2" on the 2" pipe.

If my REALLY rusty math is correct.

oooooo I get it. Actually, I thought there was more to it. I was "overthinking" it. A+ buddy..

Since when does a sewer vent need a cap?

#1 looks like you could just reef up on it and gain an inch or so. I don't get #2.

Originally Posted by John Kogel

Since when does a sewer vent need a cap?

#1 looks like you could just reef up on it and gain an inch or so. I don't get #2.

I didnt think they do but as long as they were there; just wanted to verify they received enough air volume.

Did they run DWV pipe inside of an upside-down B-vent in pic#2?

Originally Posted by Marc M

Anyone know about how much air space is necessary in front of a typical waste vent or otherwise before it becomes an issue.

"typical waste vent "

If that is a plumbing vent, the tops need to be removed and the top of the vent open to the outdoor air.

There is no reason to even consider installing a cap over a plumbing vent - it already has water in it ... it is made to get wet and have water in it.

Is that first photo a photo of broken off PVC?

The second photo, is that PVC in that B vent (as Bob asked)? If so, that is the completely wrong use and completely wrong flashing for the plumbing vent, and the completely wrong ... everything ...