An air admittance valve, or AAV, is a device used in plumbing. Not every home plumbing system has an AAV, but having one installed has many benefits.
The AAV is a cylindrical-shaped object with a noticeable lip made from PVC or polyvinyl chloride fitted with rubber valves. The valve is one-way, meaning that it only allows water to flow out and not back in.
Inside of your home, the drain-waste-vent system of your plumbing removes water from your drains and waste from your toilets and delivers these liquids to your sewer line or septic tank. The AAV's pressurized mechanism opens to allow water through the drain-waste-vent system, but then closes once the water has passed through.
Air admittance valves prevent sewer gas and odors from your septic tank from entering your home. AAVs also offer fewer parts than traditional piping systems, meaning less things to go wrong with your plumbing and reduced maintenance costs.
An air admittance valve costs $25 to $40, according to PATH (Partnership for Advancing Technology in Housing). With new construction or remodeling, AAVs offer an initial average cost savings of $293 for a 1,300-square-foot home when compared to the costs associated with installing a traditional piping system to perform the job accomplished by the AAV.
AAVs typically last 20 years, PATH reports.