The more recent design utilizes a rubber-like membrane that flexes to allow air into the drain system. It is an air admittance valve, sometimes referred to by the acronym AAV. The Studor Corporation is the largest manufacturer of AAVs, so they are often referred to as Studor® vents or Studor® valves. An air admittance valve made by Studor is shown at the top of the page, and an example of an AAV we saw under a kitchen sink at a recent home inspection is shown below.

    Two requirements for correctly installing an AAV are that it must a minimum of 4” above the fixture drain and readily accessible. Although they are rated for a minimum of 500,000 open-and-close cycles, which is approximately 30 years of usage, they do fail eventually and, occasionally, prematurely; so it’s important to be able to get to the AAV to change it out. They have a screw fitting, so switching out a dead air admittance valve is an easy plumbing chore.

    Air admittance valves can also be installed in an attic, but must be 6-inches or more above the insulation. Because an AAV requires negative pressure to open, it cannot be installed to vent a sump pump, which generates positive air pressure when operating. Also, a home’s plumbing drainage cannot rely entirely on AAVs; a minimum of one vent through the roof is required by the building code.

While we hope you find this series of articles about home inspection helpful, they should not be considered an alternative to an actual home inspection by a local inspector. Also, construction standards vary in different parts of the country and it is possible that important issues related to your area may not be covered here.
©2015 - McGarry and Madsen Inspection.


How to Look

at a House

A blog with answers
to your questions about

Mechanical Vent

More Blog Posts about Plumbing:

  1. Should I upgrade to a tankless water heater?

  2. Why does my well pump turn on and off every time I use water?

  3. How old is that water heater?

  4. My air conditioner won’t turn on. What’s wrong?

  5. Should I wrap the water heater with an insulation blanket?

  6. What’s the powdery crust on the pipe connections at the water heater?

  7. Do you check the plumbing under the floor slab?

  8. Do I have polybutylene pipe? Why is it a problem?

  9. What is causing a foggy haze on my windows?

  10. What is that big thing in the toilet tank?

  11. How do I remove cigarette odor in a house?

  12. What is the difference between water service pipe and water supply pipe?

  13. What’s the flip-up handle on the water heater for?

  14. How come the water has a rotten-egg smell in some empty houses?

  15. My well water test came back positive for bacteria. What should I do?

  16. Do you test the well water?

  17. What is the difference between a regular water heater and a power vent water heater?

  18. How do you test a shower pan for leaks?

  19. Why is my water heater making strange (rumbling, gurgling, knocking or banging) noises?

  20. What is that pipe sticking out of the ground in the yard?

  21. Why are rubber washing machine hoses a safety risk?

  22. What are the most common plumbing problems with older houses?

  23. What is a heat pump water heater?

  24. What are the common problems to look for when the plumbing has been replaced in a house?

  25. What is a dielectric union?

  26. What is the average life expectancy of CPVC pipe?

  27. What is the average life expectancy of copper pipe?

  28. What is the average life expectancy of PVC pipe?

  29. Why is a European-style bottle trap not approved by the plumbing codes in the U.S.?

  30. What is an FVIR water heater?

  31. What is difference between a single element and dual element electric water heater?

  32. What is an escutcheon plate?

  33. Is the hot water faucet handle required to be on the left?

  34. Why is a backflow preventer required on lawn sprinkler systems?

  35. What are the right words for talking about a house plumbing system?

  36. How can I tell if a house is connected to a septic tank or sewer?

  37. Is a hot water faucet required at a washing machine?

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