VENTING 101 – Air Admittance Valve Pros and Cons

Estimated reading time: 6 minutes

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. When it opens, the air can enter the plumbing system 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 won’t come out 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.

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

Some state and local building departments prohibit AAVs. Check with your local AHJ – Authority Having Jurisdiction for more info.

AAVs are certified to reliably. However, anything mechanical can and will fail. Some manufacturers claim they’re suitable for 500,000 uses (approximately 30 years).

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.

Inspecting The Studor AAV

1. STUDOR AAVs must be located at least four (4”) inches above the horizontal branch drain or fixture drain being vented.
2. STUDOR AAVs shall be accessible should replacement be required. For in-wall installation, use STUDOR recess box/grill combination.
3. STUDOR 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.
4. STUDOR AAVs must be installed in the vertical, upright position. A maximum deviation (in either direction) of 15 degrees is allowed.
5. The vent shall connect to the drain vertically to maintain an unobstructed opening in the piping to the STUDOR AAVs.
6. 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.
7. The Maxi-Vent® must be installed six (6”) inches above the highest flood level rim of the fixtures being vented in stack applications.
8. STUDOR AAVs installed in the attic area must be six (6”) inches above the ceiling insulation.
9. The use of Tec-Vent® in return air plenums shall be allowed only in engineered drainage systems designed by design professionals and approved by the local authority.
10. The maximum height of the drainage stack being vented by a MAXI-VENT must not exceed six (6) branch intervals unless used with a stack connected to a P.A.P.A. and AAVs on the branches.
11. A relief vent shall be provided when a horizontal branch connects to a stack more than four (4) branch intervals from the top of the stack. The relief vent must be located between the connection of the branch to the stack and the first fixture connecting to the branch. The relief vent may also serve as a vent for the fixture. The relief vent must connect to the vent stack, stack vent, or extend outdoors to the open air unless used with a stack connected to a P.A.P.A. device and AAVs on the branches.
12. Only Teflon® tape can be used on the valves’ threads. Using primer, solvent cement, or pipe dope will void the STUDOR warranty.
13. The Redi-Vent®, Mini-Vent®, Maxi-Vent®, Tec-Vent®, and Chem-Vent® must be installed at the finish after the system rough-in and pressure test.
14. Air Admittance Valves may be used on grease traps if they are not subject to positive pressure.
15. Other Information – Studor PDF

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