Stink from Air Admittance Vent

sniffdogDecember 27, 2008

I had one of these vents attached to the sink drain in my kitchen island. A month ago, we started detecting a smell - tought it was the garbage. AFter several attemps to stop the stink I noticed the air vent up behind the sink. I put some plastic wrap on it, held in place with a rubber band, and stink went away. Saw no impact on drainage - so I took the vent out and put a threaded plug in. Fixed!

This week detected a smell coming from a butler pantry sink. Looked underneath and saw another one of these vents. Used the same approach as above and stink went away. But this time, I can see that the water drains slower. Haven't installed the permanent plug on this vent yet.

Do i need these vents? Aren't they supposed to bring a little air in to help drainage but not let smelly gas out? Why the smell all of a sudden - is that normal? Seems odd to me that both vents started emitting the smell within a month of each other.


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The vents should not emit a smell. Time to replace them with new ones. Plugging is the very wrong thing to do.

    Bookmark   December 27, 2008 at 11:37AM
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That would be sewer gas and other food rot smells. The vents are supposed to let air in but seal from letting air and stink out.

Nicknamed cheater vents, time to get new ones as the old must have warped or rotted at the gasket.

    Bookmark   December 27, 2008 at 11:58AM
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Thanks - I will change the vents.

    Bookmark   December 27, 2008 at 5:59PM
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Yes, change them.

Do you have plumbing on an upper floor above this kitchen?

    Bookmark   December 27, 2008 at 7:42PM
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I do - but the sinks and other drains on the second floor are connected to air vents that run up to the roof. It was only these 2 sinks that had the cheater vents on them - the island sink because there is no way to vent up and the BP sink because the wall behind it does not provide an easy path to the attic.

Can someone explain what would happen if I left the cheater vents plugged forever? I plan on changing them but was curious of the downside other than slower drainage.

Thanks for the help.

    Bookmark   December 28, 2008 at 8:37AM
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Air Admittance Valves are designed to open upon negative pressure in the drainage system and close when the negative pressure is absent. If you cap them rather than replace them you run the risk of syphoning p-trap seals and allowing sewer gases to enter through the p-traps.

    Bookmark   December 28, 2008 at 9:06AM
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Thanks for the info - very helpful

    Bookmark   December 28, 2008 at 2:47PM
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Forcing them to operate under positive pressure can force the seal to leak, causing premature failure. Upstairs toilets flushing = positive pressure downstairs where they are connected to the drain. Because AAV's fail eventually they are not liked by code writing regulators and plumbers with a long view of history.


    Bookmark   December 30, 2008 at 8:07AM
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I pulled off the second AAV - made by Oatey. I guess the stink is the singal that the vent needs changing.

The house isn't quite a year old - seems odd to me that both would fail. Should I be looking for some other issue that could have caused this problem?

The second floor plumbing does not get used often - only when we have guests. We periodically go up there and flush toilets, run bath & shower heads etc to keep ptraps full.

Thanks for the help. I can't say I am fond of these AAV's but it is too late to change that so I am glad I now understand what they do.

    Bookmark   December 30, 2008 at 8:32AM
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