AAV for plumbing waste vent
dustin_7022224
| Posted in Mechanicals on
I have been reading just a little bit about air admittance valves and think they may be a good idea for our green home project. We will have a septic system and plan to have a main vent stack rise up in a faux chimney. Can we use AAVs for our branches and what are the pros and cons, other than fewer roof penetrations (which I see the value in).
Thanks,
Dustin
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Replies
Dustin,
You may find this discussion useful: https://www.greenbuildingadvisor.com/question/studor-vents-or-vent-stack
Whether and where you can use them depends on what code you are under.
No reason to have more than one roof penetration, just connect the various vents to one stack. AAVs have no place in a new build. If you actually follow the code, they cause more problems than they solve. You have to have them above the flood level, so completely pointless in the places they would actually be useful, and access is required. That means an unsightly hatch in the drywall, in a lot of cases.
Code says that only "stack-type" AAVs need to be located 6" above flood level. What exactly is a "stack-type"?
Apparently most AAVs do not need to meet the above flood level requirement and are fine under a sink.
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Stack usually refers to a vertical pipe.
So the house is being built in 3 "volumes" one of which is the garage. There bathrooms are on opposite ends of the house, there will be one in the basement, and there is a cathedral ceiling over the kitchen, in the middle of the house. I don't see any way we can have just one vent stack.
Just an anecdote: we have had an AAV for our kitchen sink for about twenty years--works fine. Done correctly, pretty bombproof.
A mixture of vent stacks and AAVs (such as the OP is proposing) seems like it avoids a lot of the potential problems that may occur with an all AAV solution. The chief ones being providing an outlet for sewer gas and equalizing pressure in the drain lines.
Yup, most likely one main 3" stack, another 2" for one of the baths and one 2" for the kitchen. I would rather have natural venting of gases rather than rely on mechanical devices for reasons stated by Malcolm. Remember mechanical vents open to let air in, so some trapped sewer gases may make its way out during the process, and you will know when.