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Table of contents
Let’s talk about air admittance valves.
Most residential building drainage systems are vented directly through the building’s roof. Here’s an example. See the white pipe peeking through the roof. The plastic pipe is “flashed” or sealed at the roof penetration to prevent rainwater from leaking into the building.
During maintenance, you’ll want to be assured the top of the vent is kept open. A blocked vent can be caused by leaves, dead animals, and ice dams (in very cold climates). Another “not-so-common” way the vent can become clogged is when a horizontal section of the venting system (inside the attic) sloped incorrectly. When that happens, it can fill with rainwater or condensation. Experienced home inspectors should be on the lookout for these conditions.
Air Admittance Valves (AAV)
Sometimes we can’t (or don’t want to) vent through the roof line. In these rare cases, plumbers use an Air Admittance Valve.
Air Admittance Valves (aka Studor vents) are built with “negative-pressure-activated” one-way mechanical valves. Used most commonly at an island sink or vanity, the vents may be used to prevent roof penetrations (as seen above) on the front roof line elevation. Think about it – when have you seen a plumbing vent on the front roof line of a home as it faces the street?
How It Operates
If we didn’t have either venting method, you would have a very noisy sink drain.
A discharge of wastewater down your sink drain causes a valve on the AAV to open, allowing the water to pass through the waste pipe. Think of it as holding a large soda, water, or milk bottle upside down and removing the cap. The liquid will come out, but not as freely as it would if you poke a small hole (a vent) on the other end of the bottle. We always want to maintain that open vent design in the plumbing system. Watch this video; they do a great job explaining it.
(Disclaimer: This guide contains my honest, experience-based advice. Some of the links below may be affiliate links, meaning I may earn a small commission if you make a purchase, at no extra cost. I only recommend sources I know and trust.)
The Pros
An AAV can significantly reduce the number of venting materials needed in a plumbing system. That’s money in the pocket of the plumber. They also allow greater flexibility in the layout of plumbing fixtures and reduce long-term roof maintenance. If we don’t have a hole in the roof, it’s easier to maintain it.
AAVs have been effectively used in Europe for more than two decades. However, there are a few limitations.
The Cons
AAVs are certified to be reliable. However, anything mechanical can and will fail. Some manufacturers claim they’re suitable for 500,000 uses (approximately 30 years). Some state and local building departments, as they mention in the video above, prohibit AAVs. Check on your local adoption for more info. This simple step is probably the most common mistake (assuming they allowed “everywhere).”
US manufacturers offer warranties that range from 1 year to “lifetime.” You’ll want to seek out the warranty info. Most plumbers won’t have it.
Note: An AAV should not be tampered with or spray-painted. I have had plumbers tell us that sewer flies and bugs have been seen at failed air admittance valves. So if you detect a sewer odor under and around your sink or in the attic, the AAV could have let you down.
Recommended Installation and Tools Needed
Recommended Installation Steps
What you’ll need (Thanks Oatey):
- Safety gloves
- Tape measure
- Pipe cutter or hand saw
- Deburring tool
- PVC primer, PVC cement or ABS cement
- Thread sealant tape
1. Remove any protective plastic film or packaging from the AAV.
2. Ensure AAV will be installed at least four inches above the horizontal branch.
3. Measure and cut pipe accordingly.
4. Chamfer and deburr pipe.
5. Solvent weld pipe to the provided adapter.
6.Wrap thread sealant tape around male threads of the AAV.
7. Insert AAV in adapter and rotate it clockwise until it is tightened securely.
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Inspecting The AAV
AAVs shall be located not less than 4 inches (102 mm) above the horizontal branch drain or fixture drain being vented. (IRC)
AAVs shall be accessible should replacement be required. For in-wall installation, use the STUDOR recess box/grill combination. During my inspections, I commonly find the Studor 20380 Recessed Box and Grill and recommend it for ease of installation. Great product.
AAVs’ location must allow for adequate air to enter the valve. An opening shall be provided in a wall or attic space lacking ventilation. Locating the valve in a sink or vanity cabinet is acceptable.
AAVs must be installed in the vertical, upright position. A maximum deviation (in either direction) of 15 degrees is allowed.
The vent shall connect to the drain vertically to maintain an unobstructed opening in the piping to the valve. Here’s what that rule means. A minimum of one vent pipe shall be extended to the open atmosphere for each building drainage system for relief of positive pressure; the size of this vent is not specified because this single vent does not determine the total aggregate cross-sectional area of the vent system. The total amount of the cross-sectional area of vents combined on the system has to equal the aggregate cross-sectional area of the building drain. When properly installed, an air admittance valve in the system is equivalent to an open vent pipe having the same cross-sectional area as any other vent. Such open-air vent is recommended, not required, to be located as close as possible to the connection between the building drain and building sewer.
The Maxi-Vent must be installed six (6) inches above the highest flood level rim of the fixtures being vented in stack applications.
AAVs installed in the attic area must be six (6) inches above the ceiling insulation.
Can the Studor Tec-Vent be used in return air plenums? If installed according to an engineer’s design and prior local code approval, the valve may be installed on sewer ejectors or in supply and return air plenums. Check it out here.
The maximum height of the drainage stack being vented by a MAXI-VENT.
Using primer, solvent cement, or pipe dope will void the Studor warranty. Use Teflon tape on the valve threads.
The Redi-Vent, Mini-Vent, Maxi-Vent, Tec-Vent, and Chem-Vent must be installed at the finish after the system rough-in because they are susceptible to damage from the testing process, and their sealing mechanisms can be compromised by the materials used in testing.
An AAV may be used on grease traps if they are not subject to positive pressure. AAVs are designed to admit air and relieve negative pressure in the drainage system, but they do not relieve positive pressure. If the system is likely to experience positive pressure, an AAV should not be used in that location.
AAV Maintenance (but we should say, replace it). If you notice sewer odors, slow drainage, or gurgling sounds, the AAV may not be operating correctly and should be checked or replaced. A damp cloth should keep dust and debris off. Don’t allow wind washing to cover the attic-installed AAV.
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Hi Gary…thanks for this informative post…I just have a few questions about AAVs in the basement when there is no venting options available..can every fixture have its own AAV?
Thank you fro this informative post. My daughter owns a home in Charlotte,NC and could benefit from your knowledge of AAV’s as she has new hot water heater and plumbing is “loud” at times of use. Her home has a master bathroom with shower,toilet a soaker tub, and 2 sinks;next to the original bathroom with a wall shower/tub, toilet ,and sink.What do you think?
Thank You for your help.
Krystal Grooters
Nice tutorial
I’m a licensed home inspector in Texas. I have ran across a situation that I can’t find a clear answer -situation I inspected a spray foamed metal frame house- all plumbing vents terminate in the attic with AAV installed. The way I interpret the IRC P3102.1-(required vent extension) says at least 1 plumbing vent stock must terminate outside- Do u know if any new plumbing code that allows all plumbing vents to terminate in the attic with AAV devices installed. Thank you for your time.
I would like to know the answer to Trent Spivey’s question — is there a new plumbing code that allows for all plumbing vents to terminate in the attic with aav devices installed.