An air admittance valve (AAV) is a one-way mechanical valve installed locally at a plumbing fixture’s site, allowing proper venting to occur without a connection to a larger venting system and stack vent. Designed to take the place of a fixture or branch vent, AAVs are an excellent alternative if you cannot connect to an existing venting system due to complex pipe-routing issues or obstructions.
AAVs allow air to enter a plumbing drainage system when negative pressure develops in the piping system (because of the flow of water). When pressure in the system is equalized (indicating that no water is flowing), gravity closes the vent terminal, preventing sewer gases from escaping into a building.
When installed correctly, AAVs are a great way to save time, money and frustration. But many plumbers decide to steer clear of them, based on faulty thinking or understanding.
Here are eight misconceptions about AAVs.
1. It's better to just penetrate the roof.
Some plumbers prefer to go straight up and through the roof, instead of trying to route the pipe internally back toward the main. In those cases, you'll often see three or four different stacks popping out of the roof. But as long as they are secondary vents, they can be eliminated by using an AAV.
AAVs open and close in conjunction with normal DWV system operation, eliminating the need to create another roof penetration. Many homeowners also prefer to avoid venting through the roof line for design and aesthetic purposes. Additionally, having fewer roof penetrations can reduce the risk of leaks over time.
In some cases, you cannot connect to an existing venting system due to complex pipe routing issues or obstructions. So AAVs offer a great alternative, especially for island sinks, remote bathroom groups, home remodels and additions that would otherwise have to be tied into a stack vent utilizing specialized venting techniques. In other words, AAVs give you and your customers more flexibility in the layout of plumbing fixtures.
2. AAVs aren't code-compliant.
The code compliance of an AAV depends on the locality or municipality. AAVs are approved by International Plumbing Code (IPC) 2012, International Residential Code (IRC) 2012, and the Uniform Plumbing Code (UPC) 2012 – Section 301.2.
But even though the national codes approve it, every locality can supersede the national codes or be stricter about the use of AAVs, requiring that all fixtures are individually vented with a traditional vent.
I recommend contacting your local municipality, building department, or plumbing inspector to determine if an AAV is approved for your particular application. If not, the fixture or drainage system will have to be traditionally vented through the home's existing venting system.
3. An AAV can be used in place of a main vent stack.
Every building needs one main vent stack exiting the roofline into the free atmosphere. AAVs do not replace a main vent requirement for the building as a whole.
I also recommend installing a relief vent when completing a new home or a large addition rough-in.
4. The AAV must be 10 feet above the fixture trap to function properly.
A common misconception is that an AAV will only work if it's 10 feet above the lowest trap. However, if it is a minimum of 4 inches above the horizontal branch drain (trap), it will function properly.
To be exact, an AAV should be located within the maximum developed length permitted for the vent. It must be located a minimum of 4 inches above the horizontal branch drain, 6 inches above any insulation material and within 15 degrees of vertical.
AAVs should not be permanently covered and should be installed in an area that allows air to enter the valve. They must also be readily accessible should the need for replacement occur.
5. An AAV can be installed outside.
AAVs are intended for installation within the confines of a structure, cannot be exposed to outside elements, and are intended for use between -40 degrees F and 150 degrees F.
Specifically, Oatey Sure-Vents are not designed for exposure to ultraviolet rays (sunlight), so they can't be installed outside. However, they can be used in an outdoor bathroom, as well as attics and crawl spaces as long as the valve is not outside (even if there is shade) and exposed to the sunlight.
Other exceptions and best practices exist for installing an AAV in an attic. That's because attics have certain conditions that can affect the AAV performance, which should be considered before choosing this location. An attic can experience drastic temperature variations depending on how it is vented and one’s geographic location. Insulation fibers can get caught inside the AAV diaphragm, making it harder for the diaphragm to open or achieve a good seal when it is in the closed position.
As an example, the Oatey Sure-Vent should be installed a minimum of 6 inches above the finished height of your insulation, and the attic must have an access point to conduct scheduled maintenance.
6. A slow drain is a sign that the AAV is not operating properly.
Some individuals mistakenly relate slow drains to the AAV not operating properly. The AAV is not the issue; the slow drain is related to a partial blockage within the drain itself.
A partially blocked drain will fill with water when the fixture is draining, and the AAV recognizes the positive pressure from the restriction and stays in a closed position to stop backflow out of the AAV. It is best to clean the drain when this occurs.
However, any AAV can malfunction or not operate properly, because it is a mechanical device. A sure sign it is not operating as intended is foul odor. If you notice a sewer smell near a plumbing fixture with an AAV installed, it could mean the AAV is not closing properly to create a positive seal and should be replaced.
7. AAVs eliminate sewer gases.
AAVs do not eliminate sewer gases. If you had an issue before you had the valve on, you’ll still have that issue, because the gas is likely coming from somewhere else.
To understand why an AAV does not eliminate gases, you must understand how it operates. Negative pressure in a DWV is created when a drain or fixture has fluids flowing through it; this is why a vent is required. Without a vent, the water would flow very slowly or not at all.
Example: Stick a straw in a glass of water and, before you remove the straw, put your thumb over the top of the straw. When you remove the straw, the water stays in the straw because there is no vent. Remove your thumb and the water will flow out of the straw because you have a vent. AAVs allow each plumbing fixture and drain to receive the needed air to drain properly.
Positive pressure is present when city sewers are relieving pressure that is designed to push back up through the building sewer and eventually out of the roof vent on a home or building. While this positive pressure is being released and plumbing fixtures and/or drains are not being used, the AAV will remain closed. This is important because if the AAV did not protect from positive pressure, a home would fill with foul odors or sewer gases.
In short, drain opening causes negative pressure. So it's drawing air in, and whenever it's not negative pressure, a rubber diaphragm in the AAV will stay closed, preventing any sewer gas from escaping.
One indication that the valve failed or is stuck is if it fails in the open position. Then you might smell sewer gas. Keep in mind that there's always sewer gas in the system, but that's what traps protect against, as well as the vent going through the roof, because the gases migrate or expel out of the vent or stay in the sewer system.
Tip: If you think the valve has failed, take a plastic bag and duct tape it around a valve for a day. If the smell goes away quickly, the valve probably failed.
8. AAVs can always be used to vent a sealed sump pit with a waste grinder pump.
AAVs can be used with grinder pumps but with exceptions. Before attempting the installation, always check with local building officials to confirm this application is approved in your municipality.
I also recommend checking with the pump manufacturer before completing the installation. Remember, you also need to vent any fixture or group of fixtures. Check with your local building official to ensure the plumbing system is designed properly before installation. If they are not vented properly, the drains will not flow properly.
You can contact the Oatey Technical Department to obtain a drawing explaining the application. The drawing outlines an alternate venting method using the Oatey Sure-Vent.
But the alternative venting method for the ejector pit/pump should not be considered as an approved application unless the local jurisdiction and the pump manufacturer do not require: (1) a dedicated vent for the pit; or (2) a vent installed into the main stack vent above the highest fixture.
Reminder: If the alternate venting method is approved, the fixture or fixture group must still be vented properly and according to your local plumbing code. The home or building owner may experience future poor venting performance with this alternate venting method if the waste line becomes partially blocked, which would restrict air/waste flow.
Watch this video for step-by-step instructions to install an Oatey Sure-Vent air admittance valve.
About the Author
Sean Comerford is a technical applications manager 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.
