Install an Air Admittance Valve

By Sean Comerford

The adage "less is more" applies to much more than life lessons. For example, in home construction and renovation, it’s crucial to eliminate unnecessary costs while keeping both efficiency and aesthetics at the forefront. Air admittance valves do just that in terms of drain-waste-vent (DWV) systems.

The DWV system consists of drain and vent pipes that remove waste from the home. While the drain-waste pipes transport waste from various drains away from the house to a public sewer or septic tank, vent pipes serve a dual purpose. Not only do they ventilate sewage gasses out of the house through an exhaust-pipe roof penetration, but they also provide an air passageway behind water through the drain-waste system. This is where air admittance valves come into play.

What Is An Air Admittance Valve (AAV)?

An Air Admittance Valve (AAV), which you may also hear referred to as a "Cheater Vent" or "Mini Vent," is a one-way mechanical valve that is installed locally at the site of a plumbing fixture, allowing proper venting to occur without a connection to a larger venting system and stack vent. There are several different AAVs on the market today that vary slightly in design; however, they all perform the same function.

AAVs offer various benefits for do-it-yourselfers, particularly when it is not possible to connect to an existing venting system or when you are aiming to reduce or avoid roof penetrations. For DIY'ers looking to avoid roof work, AAVs eliminate the need for making roof penetrations, which can be complicated and require professional help. When installed correctly, they’re a great way to save time, money, and frustration.

Important: AAVs do not replace traditional stack vents. Every building must still include at least one vent stack that penetrates the roof to relieve positive pressure within the plumbing system. AAVs are designed to complement that system, not eliminate it, by relieving negative pressure locally and minimizing the need for additional vertical vent runs.

How Does An AAV Work?

AAV plumbing operates on negative pressure activation. As water drains, air is pulled with the water as it drains, creating negative pressure. This opens the valve and allows air to be drawn into the system.

With Oatey’s Sure-Vent^® AAVs, a pressure change of -0.01psi (-0.25 inch H2O) activates the AAV to open. When that pressure is equalized, the AAV returns to its original seal, preventing sewer gases from entering the vent.

Four Factors To Consider When Selecting An AAV

Consider the following expert tips during your AAV selection and installation process.

1.     Local Code and Manufacturer Requirements

Before heading to your local hardware store, be sure to check with local municipality codes and manufacturer requirements to determine if an AAV is approved for your particular application. If the use of an AAV is not permitted, the fixture or drainage system will have to be vented traditionally through the home’s existing venting system.

2.     Sizing

You can determine which size AAV you’ll need based on the Drainage Fixture Unit (DFU) load of the fixture(s), such as an island sink or bathroom group, that it will vent. An AAV’s ability to breathe is measured in DFUs. The higher the DFU rating on the valve, the greater amount of air that can enter the Drain-Waste-Vent (DWV) system.

DFU loads are assigned to plumbing fixtures dependent on the volume rate of discharge, the duration of operation, and the time between operations. Common fixture load ratings are shown in the table below.

To ensure proper breathing capability, determine all fixtures to be vented and calculate the total DFU load, then select the appropriate AAV for the application. Proper AAV sizing is critical because under-sizing will not allow the plumbing system to operate properly.

AAVs are typically available with 1-½”, 2”, 3” and 4” adapter connections. The adapter size is based on the diameter of the vent pipe it is being installed on. Generally, a vent should be sized to be half the pipe diameter of the drain it is serving (refer to local codes for specific vent size recommendations).

Fixture Applications	DFU Load
Traditional Public Bathroom Group (Toilet (1.6 gpf), bathtub w/ shower, and sink)	6
Traditional Private Bathroom Group (Toilet (1.6 gpf), bathtub w/ shower, and sink)	5
Public Toilet (1.6 gpf)	4
Private Toilet (1.6 gpf)	3
Washing Machine	3
Bathtub w/ Shower	2
Sink & Disposal	2
Dishwasher	2
Shower Stall (5.7 gpm or less)	2
Sink	2
Drinking Fountain	0.5

*2012 International Plumbing Code

3.     Pipe Material

Additionally, verify the type of pipe material you will be connecting to the AAV adapter to ensure compatibility. In other words, AAVs with PVC adapters should only be paired with PVC pipe, and AAVs with ABS adapters with ABS pipe. Read this article to be sure you know everything you need to know about AAVs.

4.     AAV Location

An AAV should be located within the maximum developed length permitted for the vent. It must be located a minimum of 4” above the horizontal branch drain, 6” above any insulation material, and within 15 degrees of vertical. AAVs cannot be permanently covered and should be installed in an area that allows air to enter the valve. They must also be accessible in case the need for replacement arises in the future.

How To Install An AAV: Step-By-Step

Tools and Materials Needed:

●       Oatey^® Sure-Vent^® Air Admittance Valve

●       Safety gloves

●       Tape measure

●       Pipe cutter or hand saw

●       Deburring tool

●       PVC primer, PVC cement or ABS cement

●       Thread sealant tape

1. Choose the correct AAV. Check the drain fixture unit (DFU) load before installation to ensure you choose the correct AAV. This value is determined by the total amount of water that comes through a fixture. After calculating the dfu, select the appropriate aav to handle the volume rate of discharge that comes through the fixture, taking into consideration if you are venting more than one fixture. Mis-sizing your AAV can cause system malfunction.

   
   

2. Remove any protective plastic film or packaging from the AAV.

   
   

3. Ensure the AAV is installed at least four inches above the horizontal branch (wall tube). The AAV must be installed vertically with no more than a 15° angle, remaining as level as possible.

   
   

4. Measure and cut the pipe accordingly.

   
   

5. Chamfer and deburr the pipe.

   
   

6. Solvent-weld the provided adapter to the pipe. Follow these steps to achieve a perfect solvent cement joint every time.

   
   

7. Wrap thread sealant tape around the male threads of the AAV and install the adaptor securely. Make sure to fill the sink with water to check for leaks.

   
   

8. Insert the AAV into the adapter and rotate it clockwise until it is securely tightened. Additionally, ensure the AAV is not permanently covered and is installed in a location where air can freely enter the valve.

See Oatey’s step-by-step video tutorial:

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About the author: Sean Comerford is Manager, Inside Sales and Tech Support at Oatey Co. He is a third-generation tradesman with nearly 20 years of plumbing experience, including serving as the lead plumber for commercial/residential new-construction, service and fire protection jobs. He holds a State of Ohio Fire Protection License for Sprinkler and Standpipe.