In-Line Vent vs. Air Admittance Valve?

dzd9fy · Jul 8, 2010

What is the difference between these two, and what is the recommended use for an S trap in a basement lav? I am looking at the Oatey 3901 In-Line and the Oatey 39016 AAV if that helps..... Thanks!!

Oatey 39017 SURE-VENT AIR ADM VALVE, 1-1/2-Inch by 2-Inch, White

NHmaster3015 · Jul 9, 2010

If you have a S trap there is no point in venting it anyway.

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Jimbo · Jul 9, 2010

The 3901 is just an air admittance valve, el cheapo version. Make sure if you put on ANY AAV that it is installed vertically.

NHmaster3015 · Jul 9, 2010

Where would you put a vent on an S trap that would make any difference. If you vent the lateral that it dumps into it still has no effect on the S trap siphoning. If you put it at the only place that would prevent siphoning, which would be the crown of the trap, then you have an illegal crown vent.

hj · Jul 9, 2010

They are essentially the same, regardless of what they call them. You CANNOT vent a true "S" trap. You can only use an AAV to keep a "P" trap from becoming an "S" trap.

Gary Swart · Jul 9, 2010

S straps are illegal under every code, the reason being, they are not vented.

dzd9fy · Jul 10, 2010

Ok, thanks for the clarification on the differences between the two.

I am a bit confused on the comments that since it is an S trap it cannot be used, so looking for some insight here. Given the trap is where it is, has worked well for the past 10 years we have been here and guessing since the house was built [1950], what is the suggestion since this is buried under the cement?

Also, how and why would one use this valve vertically on a P trap? That makes absolutely no sense to me....

Jimbo · Jul 10, 2010

S traps used to be used, but are very prone to the trap siphoning dry, so are not allowed today. To install the AAV, you could possibly santee off the vertical, turn up with an elbow, and put the AAV there. Being below the flood rim, this could be problematic. Maybe a wye and a 45 to take if vertical? I would be interested in an inspectors take on this,

NHmaster3015 · Jul 10, 2010

The only way to do it and be compliant would be to come vertical out of the floor into a sanitary tee with the AAV on top of the tee and a P trap into the fixture. As long as the S trap remains there is no code compliant way to vent it.

dzd9fy · Jul 11, 2010

ok..... so should I just leave well enough alone? It has been working fine, I was just thinking this would be something that would be a good improvement to a less than ideal, and now not permitted use.

Thanks guys!

NHmaster3015 · Jul 11, 2010

Yep, let it be. If you notice any odor, run a bit of water in the sink. called priming the trap in the old days.

In-Line Vent vs. Air Admittance Valve?

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