Installing an Air Admittance Valve

Intro

A common problem in plumbing remodeling is figuring out how to run new vent lines when access to the existing drain-waste-vent system is blocked by some structural element.

One option is an air admittance valve. These valves are gravity-operated devices that respond to the negative pressure of draining water and open to let air in. Then gravity closes the valve, keeping sewer gases out of the room. Depending on the valve and the size of the vent, AAVs can support one or multiple vent lines. Local codes govern the use of AAVs in place of vents.

Prestart Checklist

Time
About an hour to cut and assemble five or six pipes and fittings

Tools
PVC saw or backsaw, miter box or power miter saw, deburring tool, felt-tip marker

Skills
Cutting and measuring pipe, working methodically

Prep
Sketch drain/vent assembly; clear a path for the pipes

Materials
Primer and cement for your type and size of pipe, P-trap, air admittance valve, drain pipe

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How does it work?

Air admittance valves are operated by gravity. When water and waste move down a drain line, it creates negative air pressure in the pipe. This negative pressure lifts the sealing washer and lets air in, which allows the waste to drain away freely. When the negative pressure ceases, the sealing washer falls back in place. Earlier versions of this device were spring-operated. Such units are still available but are not reliable and don't meet code in most places.

Step 1

Install the PVC drain line, the sanitary tee, and the P-trap for sink. The appropriate coupling for the AAV (glued or threaded) attaches to the tee. Check the manufacturer's instructions and local codes to determine the proper height for the AAV above the drain.

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AAV Drain line

Air admittance valves are typically placed between the P-trap of a fixture and the drain line. They are usually mounted on one leg of a sanitary tee, with the other leg going to the drain. The unit must be placed in accordance with local codes and the manufacturer's instructions.

Step 2

Depending on the type of fitting, glue or screw the AAV in place.

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Step 3

Depending on local codes and the AAV model, the completed installation should look something like this.

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