An air admittance valve (AAV) is a one-way valve designed to allow air to enter your home’s drainage system when the pressure in the plumbing system is less than the atmospheric pressure. They are sometimes referred to as an “under-the-counter” vent or “cheater” vent as well. These vents are commonly installed on a drainpipe for a fixture in an accessible location that allows air to enter the AAV, as opposed to drains that are typically connected to the plumbing system of the home that provides a venting system that terminates above the roof line.
There are some precautions to installing these however. Only approved AAV’s that are installed in accordance with the manufacturer’s installation instructions are permissible. Commonly they are used to vent fixtures:
- located in island counter tops
- fixtures that may be affected by frost closure of the vent due to local climatic conditions
- fixtures in dwellings undergoing renovation or installations where connection to the home’s traditional plumbing ventilation system may not be practical.
AAV’s should be installed above the flood rim of the fixture it is venting and in any case, no less than 4” above the fixture’s drain. in the picture shown above, failure of the AAV may allow water into the home as it is installed below the fixture (in this case, below the main floor kitchen sink in the basement).
As there are restrictions to their use, its best to check with your local Municipality to inquire whether a permit is required for the work and whether or not an air admittance valve (AAV) is permissible in your application prior to the start of any work.