Final word on Air Admittance Valves

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by gregnoob, Aug 6, 2009.

  1. gregnoob

    gregnoob New Member

    Messages:
    10
    Location:
    Virginia
    Hey everyone!

    I just finished moving my kitchen sink about 10 feet. Moving the copper and drain was fairly simple (once you forget what hours in a tiny crawl space was like). The final step is to put in the vent.

    I have two options:
    1) Put in a traditional vent that will hook up into the existing vent system
    2) Use an AAV

    Option 1 will mean running the vent outside some dry wall but inside a permanent soffit above the cabinets, then zig-zagging it down the inside of a wall (still not drywalled, contains a pass-through hence the zig-zagging)

    Option 2 calls for the AAV. This *seems* like it would be the simple solution. It is allowed in Fairfax County, VA (where I live) but the code calls for it to be installed 4" above the drain/where the s-trap meets the drain (no problem there) and a min. of 6" above the flood rim in this case of the sink. In pictures I have seen and in installation instructions that I have read, the AAV is just 4" above the drain.

    I'm looking for the pros to weight in. Is the AAV worth it? Should I just run the traditional PVC vent? If I go with the AAV, it has to be 6" higher than the maximum water level the sink can hold?

    Thanks in advance!
  2. Cass

    Cass Plumber

    Messages:
    5,980
    Location:
    Ohio
    Since an AAV will fail at some point it would be better not to install one...Since you can't install the AAV 6" above the flood rim then the hard pipe is the way it will have to go...
  3. FloridaOrange

    FloridaOrange Plumbing Designer

    Messages:
    1,317
    Location:
    SW Florida
    I think you are confusing two separate things. 4" above the horizontal branch drain. Stack type AAV's 6" above flood rim. You aren't dealing with a stack, so you need it 4" above the horizontal branch drain.

    At least that's how it reads in my code. (Florida)
  4. shacko

    shacko Master Plumber-Gas Fitter

    Messages:
    561
    Location:
    Rosedale, Md
    Vent

    An AAV is not a real vent, it is a mechanical device, they do go bad. Anytime you can get mother nature to do her magic that is the way to go. I would put in a real vent, but thats your call. :)
  5. gregnoob

    gregnoob New Member

    Messages:
    10
    Location:
    Virginia
    More Info...

    Just some pictures to show what I am dealing with. So far we're 2 to 1 against the AAV...



    1) This is how the drain pipe currently comes up. I am thinking about extending it to the red circle to leave more room in the cabinet for the disposal.




    2) These are my two options for running a traditional vent... RED option goes up and over the cabinets behind a soffit. Then it would have to turn up through the ceiling and T into the vent line there. BLUE option means more holes. The pipe is 1.5" so holes shouldn't be too bad.




    3) BLUE connection to existing vent network




    4) RED connection


    So, any thoughts? RED, BLUE or AAV? And should I move the drain to come through the base?

    Thanks,

    Greg
    Last edited by a moderator: May 31, 2012
  6. FloridaOrange

    FloridaOrange Plumbing Designer

    Messages:
    1,317
    Location:
    SW Florida
    Just to clarify, I'm not really for AAV's but if you can't get a natural vent out then that's the next option.
  7. SewerRatz

    SewerRatz Illinois Licensed Plumber

    Messages:
    1,705
    Location:
    Chicago, IL
    I would run the vent pipe. Never been a fan of AAV's they go bad, also the only allow air into the venting system , they are no good for when there is a positive pressure in the DWV system.
  8. Gary Swart

    Gary Swart In the Trades

    Messages:
    7,342
    Location:
    Yakima WA
    There is no final word on AAVs. Some licensed plumbers use them in certain situations and some plumber curse them as the devils inventions, and that's not going to change. Certainly they are not be preferred method of venting, but they do work. As noted, they are mechanical devices therefore they can fail. That's why they can not be buried in a wall. I'll not argue the previous posters statement that they are not vents, but if it has long ears and hops like a rabbit, it probably is a rabbit.:) I hope you do not plan on having a true S trap. S traps have been illegal in most codes and jurisdictions for many years. The correct trap is a P trap.
  9. gregnoob

    gregnoob New Member

    Messages:
    10
    Location:
    Virginia
    Well thanks to everyone for the advice... Looks like I'm running the traditional vent!

    So... blue route or red route?

    Also, for ease of putting in the P trap and disposal, should I move the drain pipe so it comes out of the wall?
  10. Rich B

    Rich B DIY Senior Member

    Messages:
    283
    Location:
    New Jersey
    Since I was involved a little in some earlier posts about AAV's......I will tell you what I did. As I said in those earlier posts...there are no proper indvidual vents on any fixtures in my 50+ year old two story two family duplex home. There is one main vertical 4" stack and a horizonatl branch on the second floor for the back to back bathrooms. No vent of any kind on the kitchen sinks or the basement washing machine drains. I think they decided when they built the place it was all wet vented by the stack but it really was improperly done. I redid the kitchen drains in PVC all the way to the main stack and there is just no way to get a vent up from that kitchen sink without alot of demolition of walls and up thru 2 stories. I added the AAV.... a Studor and it has worked with no issue of any kind for at least 2 years. No odor and the drain works better than ever as the old galvanized pipes were real bad inside....I can change that Studor valve in about 5 minutes if I had to.....It is not above the flood level of that sink but is higher then the requirements stated in the Studor install guide. I put it as high as I could get it and still be able to service it......I did also redo the basement washing machine drains and was able to put a proper vent in for those as I had a path thru some open walls. There is no way I could get that kitchen sink connected into that vent or I would have done it.....

    I do have a 4" cast iron vertical stack that goes thru the roof.......so the odds of having a positive pressure act on the Studor valve sounds pretty unlikely.....
    Last edited: Aug 6, 2009
  11. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,540
    Location:
    Cave Creek, Arizona
    Aav

    Calling it the "final word on Air Admittance Valves" sounds like one of those Johnny Carson/Ed McMann routines where he is going to tell him EVERYTHING he needs to know. Positive pressure with an AAV often occurs when there is a stoppage problem elsewhere in the system. Without proper diagnosis, you will try to get the sink flowing by snaking its drain, when the real problem is elsewhere. This can lead to immense frustration after you snake it a dozen times and it still doesn't drain. Then you come here and ask why your snake is not working. This would be a common problem with a flooded septic system, which would not create a problem anywhere else in the house where there is a regular vent.
    Last edited: Aug 7, 2009
  12. SewerRatz

    SewerRatz Illinois Licensed Plumber

    Messages:
    1,705
    Location:
    Chicago, IL
    I wonder if the people that giving glowing reviews of the studder vents are plumbers that went through 4 to 5 years of training and 4 years of schooling. As well as taking 4 hours of continued education classes. Also if they have any field experience.

    They do not work properly all the time, it is a hack way of doing plumbing. Why do you think half of the states do not allow them. Why do you think that the other half of the states that do allow them over half of them you have to get approval to use them from the building department.
  13. Terry

    Terry Administrator Staff Member

    Messages:
    14,946
    Location:
    Bothell, Washington
    The family had a mobile home in Mattawa Washington, with an AAV in one bathroom.
    For less then the cost of a fitting or two, they could have hard vented, and then we wouldn't have dealt with the smell from that bathroom, until we realized it was a bad AAV.
    You don't have maintenance issues like that with proper venting.

    Any mechanical device made with rubber will fail.
    They need to be accessible and with proper ventilation.

    The valve only works with pressure in one direction.
    Plumbing provides pressure in two directions.

    If there is not other way, I can see it,
    But when you have the option during rough-in of hard venting, then hard piping is the way to go.
  14. nhmaster

    nhmaster Master Plumber

    Messages:
    3,189
    Location:
    S. Maine
    Probably won't be, but that should defiantly be the last word :rolleyes:
  15. gregnoob

    gregnoob New Member

    Messages:
    10
    Location:
    Virginia
    Thanks everyone! I took your advice and went with the hard venting. It was actually a lot of fun running all the turns to get it up around the pass-through window!
  16. Cass

    Cass Plumber

    Messages:
    5,980
    Location:
    Ohio
    I hope you did not cause a trap any where in the venting system as it willl defeat the whole purpose of the vent...I have not looked at any drawings but your statment

    "It was actually a lot of fun running all the turns to get it up around the pass-through window!

    Gave me pause to think you may have...

    Incorrect pitch can trap it also...
    Last edited: Aug 15, 2009
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