Standard plumbing vents vs. air admittance valves:
Above: a conventional plumbing vent stack termination above the roof line.
If a plumbing drain is not vented to the atmosphere drain performance is likely be slow and noisy. Worse, the vacuum created by water passing through the drain waste piping system can cause water to be siphoned out of plumbing fixtrure traps. The loss of that trap water will in turn permit potentially explosive sewer gases to enter the building.
Typical “standard” plumbing systems include a plumbing vent pipe that passes up through the building roof and terminates above it.
Note: An AAV should 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.
If we didn’t have either venting method you would have very noisy sink and toilet drains. A discharge of wastewater down your sink drain causes a valve on the AAV to open. When it opens air is allowed to enter the plumbing system. Watch this video to help understand how a plumbing vent works.
Some state and local building departments prohibit AAVs. Check with your local AHJ – Authority Having Jurisdiction for more info.
An AAV can significantly reduce the amount of venting materials needed in a plumbing system. That’s money in the pocket for 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 the roof. AAVs have been effectively used in Europe for more than two decades. However, there are a few limitations.
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.
Air Admittance Valves vs “Cheater Vents”
Where a conventional plumbing vent system is not available or not feasible the local plumbing inspector may permit an air admittance valve to be installed.
An air admittance valve is designed to allow air in to the drain piping system to which it is connected whenever pressure in the drain system is below atmospheric pressure outside the valve.
Photo: an older style “cheater vent” that is spring-operated
Watch out: the “Cheater Vent” shown above uses an internal spring that opens and closes the DWV seal. Studor, in their TECHNICAL MANUAL (cited and linked below) point out that this type of air admittence valve, or “old style” valve is not legal and does not meet any of the plumbing codes.
It may also be unsafe as a weakened or jammed or broken spring in the valve can lead to a failure that admits dangerous sewer gases into the building.
[Click to enlarge any ] Shown above: an older (now obsolete but still sold) V-200 air admittance valve
Air admittance valves (AAVs) also have to withstand the positive pressure that can occur in some public sewer systems, in forced-main public or private sewer or septic systems, in plumbing drain systems using a sewage ejector pump, or in a blocked private septic system or in systems located in hilly terrain.
Where high sewer gas pressures are anticipated, the sewer piping system should include a vent to the building exterior. (Studor 2016)
Some plumbing literature describes AAVs as P.A.P.A. devices. However they are different.
An AAV admits air into the system when under negative pressure. A P.A.P.A. or Positive Air Pressure Attenuator (described in more detail below) handles temporary back-pressures or positive air pressures in the drain/waste/vent piping system.
And some suppliers (National Builders Supply) recommend locating AAVs or PAPA devices throughout the plumbing system to improve drain performance by handling variations in air pressure in the drain-waste-vent system (DWV system), and to avoid trap siphonage.
Watch out: If you smell sewer gases in your building conditions could be dangerous (risking a methane gas explosion) or unsanitary.
See REMEDIES for SEWER ODORS, PLUMBING and
Air Admittance Valves retail for prices between about $6.00 and $32.00 U.S.D.
Shown just above is a black plastic mechanical air admittance vent from Keeney and retailing about $6. Youll note that it looks a bit like the V-200 shown above.
Watch out: mechanical or spring-operated AAVs are not IPC code compliant and are not recommended.
Below: a Studor® Mini-Vent Air Admittance Valve (Code-Compliant).
However this Studor vent may not have been installed sufficiently high above the horizontal drain line. Details are given in the Studor Technical Manual and vent installation instrucitons provided here.
According to Studor, the companys Air Admittance Valves (available in several models and capacities) open when the drain system senses negative pressure as low as 0.1 psi, but will remain closed at 0 psi or above.
This vent is designed to open when the plumbing fixture(s) it serves are draining, thus allowing air to enter the drain waste vent system.
The Studor vent AAV closes (by gravity alone, no springs), when there is no wastewater flowing through tye system, thus preventing sewer gas from passing up the drain or vent into the building.
According to Studor “This style air admittance valve is not recognized as a mechanical vent in the International Plumbing Coder (IPC).” – op. cit.
Exerpting from the Studor manual:
Because AAVs are either at or very near the Point Of Need (PON) for air, and thanks to their reaction times, a system utilizing STUDOR AAVs is capable of balancing its internal pressure much more efficiently, without trap movement or depletion than open pipe vent systems.
This is particularly true in large commercial applications where the air needed to balance the system after each occurrence is drawn from far away points and thus require substantial time to reach the Point Of Need (PON). – op. cit.
What is the point of a Studor vent?
How long does a Studor vent last?
What happens when a Studor vent fails?