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Community and Q&A

Studor vents or vent stack?

jackofalltrades777 | Posted in Building Code Questions on

I was told by a plumber today that the local code allows for Studor Vents instead of the old tried & true plumbing vent stack. The Net Zero homes they are doing are cutting back on the holes in the roof and the plumbers are using Studor Vents.

On my custom build, should I go Studor or old school vent stack (one 2″ stack through the roof)?

Any cons to the Studor?

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  1. GBA Editor
    Martin Holladay | | #1

    Studor is a brand of air-admittance valve. The worry, I suppose, is that the spring will eventually fail and the valve will stop working.

    Traditional plumbing vents have no moving parts, so I favor the traditional approach.

    A plumbing vent has no connection to the interior air of a home, so there shouldn't be any air leakage associated with a traditional plumbing vent, as long as the penetration is properly sealed. There will be some conduction losses through the PVC or ABS pipe, but these conduction losses aren't very significant.

    -- Martin Holladay

  2. Expert Member

    The more passive systems like venting you make reliant on mechanical devices, the more potential problems you are introducing into a build. Whether that matters to you depends on your appetite for risk.

    Bad AAVs don't really do much more than make your house smell until you figure out what the problem is, but to me they are a solution in search of a problem. I don't use AAVs anywhere. On islands I use a loop vent. When the plumbing is complete I never need to think about it again.

    If you do use AAVs, ask your plumber to attach them to the stack with flexible rubber couplings so that you can easily change them if they fail. Cutting out an AAV up under a kitchen sink is awkward at best.

  3. Anon3 | | #3

    There's a lot of warnings about AAV on the net, read some of them.

  4. onslow | | #4

    Just ended my first full year in our new pretty good home that is fully fitted with AAV vents. I must have missed all the dire news regarding them, so I went all in, with just one side stack location to avoid any roof penetration. Given our bath/laundry/kitchen layout and our insulation and roof choices the AAVs provided a flexibility that I found useful. The plumber didn't like them (and his installation care showed that), however no performance problems have displayed themselves beyond the small sucking noise they make. Since a toilet flushing is considerably louder, the noise is seldom noticed or commented on even by visitors.

    The state code here allows for side wall vent locations within certain parameters which could be tough on a city lot. We are on a big lot so no problem other than wind issues which sometimes can cause a bit of a stink at ground level. A traditional stack might have allowed odors to waft upward. Code here demanded that the one device not to be allowed on AAV was the laundry hookup point. Luckily that run was easily chased up two floors and out the side wall.

    The only caution I might point out is planning for the placement of AAVs. Our circumstances resulted in two scenarios.
    One scenario looks like a standard vertical vent run terminated with an AAV. The cleanest method is to use the Studor integrated vent/wall boxes (available on Amazon) and place the access face in an adjacent closet up high. Remember to account for the drywall, trim and any shelving while placing. The AAVs just unscrew for replacement. I don't think flexible couplers would pass in many localities.

    The second scenario regards placement under kitchen sinks or in small vanities. This can get to be a delicate dance with the fittings glue-ups placement and faucet chosen. There is a wall of windows over our kitchen counter, so like an island location, the traditional loop venting might have worked if we were willing to risk a boot on a metal roof. Framing, headers and other reasons would have made all attempts to connect with other vent lines in a standard set up very tricky. The AAV simplified things a lot. In fairness, placing the AAV location for access and not getting cross-wise of the hoses, garbage disposal, dishwasher trap and spray hose loop can be a bit trying. The really small upstairs vanity provided further tests of my shoe horn techniques.

    Just the same I wouldn't have gone with the traditional vent lines based on prior experience with them in a northern climate. We had two sizes after a remodel, a two inch and an old style iron 4" with the lead boot flashing. Both would clog up frost and cause issues when we had very cold temperatures. The pitch of the connected vent lines did not prevent warm moist air from getting to the vertical exit. Perhaps a flaw of that house only. I would look at your own plan with the plumber, if he is willing and thoughtful, to make the call. The AAV technology has been around a long time.

  5. Anon3 | | #5

    One of the purpose of the vent is to vent toxic gas, AAV does not do that. When they fail, the toxic gas goes in the house and some are odorless.

    Also, watch the AAV death video on youtube, pretty eye opening.

  6. Expert Member

    Our code requires that AAVs be installed above the flood height of the fixture they serve. In practice this often means locating them behind the sink where unscrewing them for replacement is difficult or impossible. I'm curious as to which plumbing codes preclude rubber couplings on drain lines under sinks?

  7. SwitchgrassFarmer | | #7

    If I had a "do-over", I would have put in a simple vent stack. We jumped through too many hoops to avoid avoid roof penetrations through our SIP-ventilated airspace-metal roof assembly. However our plumber was worried about those penetrations, and so was I. Consequently, like Roger, we used a mixture of AAVs and sidewall vents.

    From the AAV perspective we had a few locations where other solutions would have been near impossible. For instance our kitchen sink was in an outside wall/window location, and the second floor bathroom vanity was on the other side of a post that supports our ridge beam, so we used AAVs on these.

    I have no complaints on the AAVs. It's the one large main sidewall vent and one small sidewall vent that complement them that I regret. These sidewall vents, placed in locations that are "code distance" away from operable windows, stink, literally.

    Yes we too have faced the occasional septic smell problem, worst on summer mornings when cold air sinks down the hill towards our little valley and puts a "lid" above us. That is unfortunately also one of the times when it would be nice to open a window. Funny thing is I knew before we built the house that we would be able to take advantage of this downward cool air flow. I never connected that it could also work against us.

    We tried four fixes; I will give each a "score".

    *The first fix was to add a charcoal filter equipped vent cover on the septic tank riser. Shifted some of the smell origination a little farther downhill to the tank area, but still under the "lid", and so you could now also smell it when you walked down our lane. Score: C

    *The second fix was to apply in line charcoal filters to each of the sidewall vents. Helped by the house some, but not dramatically. Score: C+

    *The third fix was to install a whole house trap at the entrance to the septic tank. It's a total cure by the house. Score: A-

    *The fourth fix was to re-seal the top of the septic tank riser and ... wait for it ... put an AAV on the tank side of the whole house trap. Smell is now mostly undetectable. Score: A

    So we are at a place where 99% of the time the septic smell issue is handled. Unfortunately there are still occasions, like when I run a couple loads of laundry in a row when the wind is "just right" (or maybe that is "just wrong"), that the smell can be detected outside. I am thinking of trying to flare it off next!

    Anyhow, in hindsight, I am sorry we didn't just run the darn vent lines through the roof. Would we have still had a problem in our little "valley"? I guess we will never know that.

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