How to Install an Air Admittance Valve to Fix a Slow-Draining Sink

Discover everything you should know about air admittance valves (AAVs) and how you can install one yourself to save time and money.

Butcher Block counter top
Photo: Jay Wilde
Project Overview
  • Total Time: 2 hours
  • Skill Level: Beginner

A common problem in plumbing remodeling is how to run new vent lines when a structural element blocks access to the existing drain-waste-vent system. It might seem like all hope is lost, but don't let that minor roadblock get in the way of your dream kitchen makeover. One solution is an air admittance valve or AAV. 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. However, before you begin installing an air admittance valve, check with your local building inspections office, as local codes govern the use of AAVs in place of vents.

how to install an air admittance valve

BHG / Michela Buttignol

What You'll Need

Equipment / Tools

  • PVC saw or backsaw
  • Miter box or power miter saw
  • Deburring tool
  • Felt-tip marker

Materials

  • Primer and cement for your type and size of pipe
  • P-trap
  • Air admittance valve
  • Drain pipe

Instructions

  1. Understand How Air Admittance Valves Work

    Before you install one, it's important to understand how AAVs 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 unreliable and don't meet code in most areas.

  2. air admittance valve illustration
    Illustration by Art Rep Services, Inc.

    Determine Placement

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

  3. pipe with air admittance valve

    Install PVC Drain Line

    Install the PVC drain line, the sanitary tee, and the P-trap for the 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.

  4. pipe with air admittance valve

    Attach Air Admittance Valve

    Depending on the type of fitting, glue or screw the AAV in place. Look to the manufacturer's directions if you need additional assistance.

  5. pipe with air admittance valve

    Check Work

    Depending on local codes and the AAV model, the completed installation should look like this. AAVs must always be installed vertically and should be unobstructed from items under the sink.

Related Articles