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Old 09-15-2011, 09:34 PM   #1
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AAV in a DWV system with a septic tank


Hi, I would like to use AAV's in a few locations in a new residence that will have a septic tank. The instructions for the Oatey product says: "Sure-VentŪ AAVs can vent a building with a septic tank provided the system is satisfactorily connected to the atmosphere (see local codes). The first chamber of the septic tank must be fresh air vented." And that this is "a common model code system requirement".

Can someone explain this further? Doesn't venting the tank defeat the anaerobic action? Are there special products for the vent or is it just a dumb PVC pipe from the first chamber to the surface? Is this vent to defeat positive or negative pressure or both?

I can find very little on the internet about this.

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Old 09-16-2011, 02:18 AM   #2
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AAV in a DWV system with a septic tank


I'm not a pro plumber and I don't know the code regarding AAVs, but I've had an AAV on my downstiars bathroom vanity sink drain since I built this house in 1977. My house is on a septic system and the only venting is the normal DWV vents on the house. Works great. Never had any problems with it. Don't know why you should.
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Old 09-16-2011, 08:53 AM   #3
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AAV in a DWV system with a septic tank


I just talked with a local manufacturer of septic tanks. He said that if my DWV system has the main vent thru the roof to fresh air that my tank is already fresh air vented. This is good enough for me.

I thought they were referring to a short pipe running directly from the top of the tank to the open air. I guess not. I will check with Oatey and see if they have anything to add.
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Old 09-16-2011, 10:22 AM   #4
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AAV in a DWV system with a septic tank


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Originally Posted by Mike Swearingen View Post
I'm not a pro plumber and I don't know the code regarding AAVs, but I've had an AAV on my downstiars bathroom vanity sink drain since I built this house in 1977. My house is on a septic system and the only venting is the normal DWV vents on the house. Works great. Never had any problems with it. Don't know why you should.
Mike
Same here. But check local code - AAVs are not legal everywhere.
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Old 09-19-2011, 06:27 PM   #5
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AAV in a DWV system with a septic tank


Nope. A direct septic tank vent is what they want. This is the response from Oatey:

Quote:
The tank itself needs to vent methane gas into the air. This is usually done by a vent to the tank with a 180° or two 90° fittings to point the vent towards the ground.

The reason for this is that the methane gas can deteriorate the flapper in the AAV and needs to be released from the system before it can back up into the vent stack.

Please let me know if you have any further questions.

Thank You,

Oatey SCS Technical Team
(800) 321-9532
My concern now is whether my health department will tolerate the vent.
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Old 09-20-2011, 07:58 AM   #6
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AAV in a DWV system with a septic tank


That's just nuts. Never heard of such a thing. I surely wouldn't want my yard to smell like s***.
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Old 09-20-2011, 08:42 AM   #7
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AAV in a DWV system with a septic tank


Yes this requirement opens a huge can of worms:

1) The stink --like you said. Solution: a big activated charcoal filter at end of the candy cane?
2) Will the vent degrade the anaerobic action of the septic tank? Probably not. Methane is lighter than air. It's going to travel up the line and out of the stack anyway.
3) Will lightning someday ignite the methane and burn the forest down? Don't know. I doubt the concentration is high enough.
4) Methane is 22 times more potent than CO2 as a greenhouse gas. See #2 (no pun intended).
5) Do I want to see a big white candy cane sticking out the top of my tank? Well I guess it could be camouflaged.
6) Do I want to field "What the f**k is that?" questions for the rest of my life? No.

I will submit (most) of these questions to that tech support guy. Will post the results here.
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Old 09-20-2011, 08:53 AM   #8
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AAV in a DWV system with a septic tank


See what these Studor guys have to say. That sounds like overkill to me. I don't know why a septic system would be much different than a sewer system. They both have methane gas and they both are vented to the air by the same DWV systems.
www.studor.net
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Last edited by Mike Swearingen; 09-20-2011 at 08:57 AM.
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Old 09-20-2011, 09:02 AM   #9
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AAV in a DWV system with a septic tank


Forget about me asking again. I'm just going to skip the tank vent and when and if the flapper degrades I'll just replace the AAV. So few people around here have even ever heard of an AAV anyway, I can probably get away with it.

I would add one more thing to the can of worms list above:

7) What if the health department doesn't like the vent?

OK. Thanks all. May future souls benefit from this post.
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Old 09-20-2011, 09:29 AM   #10
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AAV in a DWV system with a septic tank


Mike, I found a 18-page PDF at Studor (which was not searchable so I had to skim it). Couldn't find any reference to a separate septic tank vent. Just FYI. So it probably is overkill.
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Old 09-20-2011, 11:53 AM   #11
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AAV in a DWV system with a septic tank


I don't know about Oatey AAV design and construction, but I've had the same Studor AAV on my downstairs bathroom sink drain since I built this house in 1977 and have never had a problem with it.
I don't care WHAT someone tells me, I am NOT going to vent my septic tank at yard level.
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