Air Admittance Valve AAV Troubleshooting
AAV Repairs: Slow drains, noises, test procedure

AAV Air-Admittance Valve Noise Diagnosis

Several readers have reported odd noises traced to Air Admittance Valves or Air Admittance Vents. We collect them here to provide some noise diagnosis suggestions.

Above on this page we've already explained that adequate plumbing vents not only help drains to empty properly, they also avoid drain noises like the familiar glub glub sound of a slow drain.

Also see these

Air Admittance Valve noise diagnostic tools

• CLICKING SOUNDS
• PLUMBING DRAIN NOISES
• PLUMBING NOISE CHECKLIST
• PLUMBING SYSTEM NOISE DIAGNOSIS & CURE - home
• POPPING SNAPPING NOISE DIAGNOSIS
• TEMPERATURE CHANGE RELATED NOISES and for a common example
• TAPPING NOISES in BUILDINGS
• TICKING NOISE DIAGNOSIS
• TICKING NOISES

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On 2021-12-01 by Inspectapedia Com Moderator (mod) - diagnose air admittance vent clicking noises

@Jane,

Noises coming from an air admittance valve or AAV could be caused by a leak into the building drain system somewhere that is causing intermittent air admittance through the AAV - check for subtle leaks like a hard-to-spot running toilet.

Other possible causes of AAV noises are described at

PLUMBING VENT NOISE https://inspectapedia.com/plumbing/Plumbing_Vent_Noise.php

and a remarkable honking or kazoo noise has been traced to AAVs too, as described by Ken Smith · Sept 30, 2021 in a reader post currently found
at PLUMBING VENT NOISE FAQs https://inspectapedia.com/plumbing/Plumbing-Vent-Noise-FAQS.php

He said

I've a non-predictable whistle, kazoo-decompression sound coming from the attic. Studor vent does not go through the roof. It sometimes becomes more frequency during heavy or long-duration storms. Could it be the Studor vent? Or?

Thermal expansion and contraction can also produce plumbing noises including clicks and ticks, particularly if a drain line is
installed without any clearance space where it passes through other building materials.

You might find thermal expansion/contraction noise sources by visual inspection for tight plumbing passages, by relating the time you hear the noise to temperature changes in or outside the building, even wind, and also by using a mechanic's stethoscoope.

Thank you for a helpful question. Please do keep us updated on your progress with this admittance vent noise diagnosis as that will help other readers, and as you may be able to report more observations that will let us offer more suggestions.

I'll collect all of our AAV or admittance valve/vent noises onto this page.

On 2021-11-30 by Jane - Why does our air admittance vent make a ticking sound

Why does our air admittance vent make a ticking sound

On 2019-04-26 by Nick Loche - dripping noise diagnosis at an air admittance valve

@Douglas Rome,

Does the drip noise you describe only occur when you are running water? If this is the case it could possibly be that water pipes are expanding against the holes that the pipes run through and you could wind up chasing a phantom sound forever. If the holes that the water pipes run through are too small or the strapping used is too tight around the pipe this could possibly produce that same sound similar to a drip.

I also agree with [the moderator] in that the AAV must always be accessible.

If it is the AAV one possibility is that the tapping is the valve opening and closing making a noise and in this case run hot water at a very slow but steady stream for 5 minutes and if there is no tapping at all then run the water fully open and if the tapping begins then it is more possibly the AAV Oatey valve making the tapping noise.

Also see DRIPPING WATER SOUND SOURCES - described as tapping

On 2017-04-23 by (mod) - never bury an AAV

I'm not sure it's good practice to bury an AAV in part because it can't be inspected nor replaced if it fails. Also, covering an air admittance valve might block air entry into it, causing drain malfunctions that can be unsafe.

The hazards include more than just poor venting or poor drains: an AAV that jams may also vent dangerous sewer gases into the building. The valve must remain accessible.

I like the stethoscope approach; also look for stains below the area where you hear dripping.

See DRIPPING WATER SOUND SOURCES - described as tapping

On 2017-04-23 by Douglas Rome - our AAV is buried behind drywall but we hear dripping sounds

we did a 1st floor kitchen remodel and had to use an AAV to accommodate a second floor lav. the walls and ceiling were open for a few weeks after the AAV install. in that time we did not notice a leak in the exposed lav piping.

The tapping sound we hear is like you would hear if there was a slow leak and water dripping on drywall ceiling drip drip drip.

The AAV is buried behind drywall and it is a Oatey brand I don't recall the model number it was purchased at one of the big boxes. I will try a stethoscope to see if I can pinpoint. thanks, douglas

On 2017-04-17 by (mod) - AAVs do not normally make noise

Douglas

The AAVs I've installed, seen, inspected were rather silent. If you hear a tapping sound and it's for sure coming from the AAV (try a mechanic's stethoscope) then perhaps the valve is indeed sticking or defective.

On 2017-04-17 by Douglas Rome - tapping (dripping) sounds at AAV?

does a AAV make noise? Like a tapping sound while water
is flowing in the drain? Thanks, Douglas

Air Admittance Valve AAV Slow Drain Diagnosis

On 2019-08-14 by (mod) - diagnose slow drainage with an AAV installed

I don 't think shortening the sink drops (what I call tailpieces) will help this problem - though an experiment would be interesting.

Illustration: Studor's Mini-Vent® DFU (Drain Fixture Unit) sizing chart from the STUDOR PRODUCTS MANUAL cited and linked-to above. Studor's Tec-Vent® has the same DFU capacity. Other Studor brand AAVs vary in DFU capacity - more charts are given below.

[Click to enlarge any image]

Your theory about the AAV being too big is interesting too, but I'd be surprised if that's the trouble since the designer of the larger-capacity AAV has to consider that the AAV has to open at lower drainage rates than the maximum that the vent can handle. Your AAV could be too-small, however as we'll discuss here.

Typically an AAV opens at - 0.1 psi and closes at 0 psi or above.

According to the Studor AAV Sizing chart on the label you attached, assuming your kitchen sink drains are 2" diameter your AAV can handle 6 DFUs - more than enough for just two kitchen sinks.

Curiously your Studor Vent label shows a "blank" for the maximum number of DFUs ifyour drain horizontal branch is just 1 1/2" - so your AAV could be too small, but not too big.

Let's both look over the specs some more and let's review the reasons that a drain line may be slow when an AAV has been installed.

Causes of Slow Drains where an Air Admittance Valve AAV is Installed

1. Downstream trap:
   
   The most common cause of poor or slow drainage where an Air Admittance Valve has been installed is back pressure in the drain piping system. That can be caused if the AAV has been installed upstream from a drain that is trapped.
   
   The trap downstream from the AAV combined with wastewater flowing down the drain when the AAV-supported fixture is being drained (such as a toilet or large sink) can cause back-pressure that prevents the AAV from opening enough for the drain to flow freely.
2. Downstream drain blockage:
   
   A second problem that will cause poor drainage when the AAV is installed is a partial drain blockage downstream, usually pretty far downstream, from the fixture being served by the air admittance valve.
   
   An improperly-sloped drain line can also cause the same slow-draining AAV problem as a remote drain blockage. Positive pressure in the drain line.
3. Missing or blocked conventional roof vent
   
   on the main drain line into which the AAV-served drain ultimately empties. A roof vent may be blocked by debris, frost (in freezing weather), and even a frog (at least I found one there once).
   
   Oatey and Studor make clear that while it is helpful (and sometimes permitted) to install an AAV at a fixture that's otherwise too distant from the building vent system (example would be a kitchen island sink drain or garbage disposer drain in an island sink), the building drain system into which the fixture ultimately empties must be served by a conventional roof vent.
4. Subtle partial drain blockage
   
   (uncommon) such as a horizontal plastic trap arm that is pushed so far into a drain tee or sink tailpiece tee that it is partly blocking drain flow - similar to #2 above but usually closer to the fixture.
5. AAV too small for the total wastewater volume:
   
   compare the DFUs (drain fixture units) number with the number of fixtures actually being served by the AAV.
   
   Watch out: In Ryan's sink photo below we see two kitchen sinks draining into a common trap line with a Studor Mini-Vent® AAV installed.
   
   While Ryan's photo of the Studor Mini-Vent label shows a blank at the "Maximum DFUS" column for the 1 1/2" diameter drain line, the company's technical product manual (PDF given above in this article) shows that on a 1 1/2" diameter horizontal drain, the Mini-Vent can handle a MAXIMUM of 3 DFUs.
   
   If Ryan's AAV is installed on a 1 1/2" diameter drain, that AAV may be too small when both sinks are draining at once, as we count 2 DFUs per kitchen sink. If it's installed on a 2-inch diameter drain, it should be OK and the slow drain problem is elsewhere.
   
   See details at PLUMBING DRAIN FIXTURE UNITS DFUs
6. AAV not installed according to the manufacturer's specifications.
   
   See examples of those details, such as installed with insufficient height above the horizontal drain, installed too far from the vent stack, not installed vertical, etc. in the article above.

Positive Air Pressure Attenuators

If you cannot solve your positive drain pressure problem and are confident that there are no drain bellies, improper slopes, improper sizings, blockages, vent defects, then you might try installing a positive air pressure attenuator such as Studor's P.A.P.A.™ intended for commercial use. Here is an excerpt from the Studor technical manual cited above:

The P.A.P.A. device is the perfect complement to STUDOR Air Admittance Valves. Together they form an Engineered System known as “Studor Single Pipe System (SSPS)”, a total solution to building venting requirements.

The Studor AAVs deal with negative pressure in the system while the P.A.P.A. effectively deals with the positive pressure transients. The combination of the two maintains the perfect system balance quickly and efficiently throughout the system preventing siphonage and blowing of traps. 

Be sure to review the technical specifications, limitations, and instructions in Studor's technical manual.

I'm going to copy this conversation over to the home article where it may invite helpful comments from others

AIR ADMITTANCE VALVES AAVs inspectapedia.com/plumbing/Air_Admittance_Studor_Vents.php

Well anyhow that's a better trap installation that's less clog likely.

When no air is being drawn IN through the AAV that suggests that the drain is functioning even without air admittance (that can happen though it's not long term reliable) - but you say that with the AAV removed the drain works better. That suggests that the AAV isn't admitting enough air fast enough. (Or less likely there's a downstream blockage).

Often on a two-sink setup I notice that when the big sink is draining air is drawn into the drain through the smaller one - that tells me that there isn't a good air flow into the drain system through the building plumbing vent piping - which is why you added the AAV in the first place.

I'm adding a stack of PDFs on AAVs and their specifications and air admittance valve installation instructions from various manufacturers so that we can review their specifications;

On 2019-08-14 by Russ

For what it is worth, here is a pic of the container the AAV valve came with. It's hard to see the 1 1/2" but it is 3 DFU's max.

I have wondered if the AAV I have is too large for this application but wanted to reach out for advice before buying another brand to see the results. Going back to your original reply, I can shorten the sink drops to raise the assembly too.

On 2019-08-14 by (mod) - Troubleshooting a Studor AAV that causes too-slow drainage

Well anyhow that's a better trap installation that's less clog likely.

When no air is being drawn IN through the AAV that suggests that the drain is functioning even without air admittance (that can happen though it's not long term reliable) - but you say that with the AAV removed the drain works better.

That suggests that the AAV isn't admitting enough air fast enough. (Or less likely there's a downstream blockage).

Often on a two-sink setup I notice that when the big sink is draining air is drawn into the drain through the smaller one - that tells me that there isn't a good air flow into the drain system through the building plumbing vent piping - which is why you added the AAV in the first place.

I'm adding a stack of PDFs on AAVs from various manufacturers so that we can review their specifications;

See AIR ADMITTANCE VALVES AAVs https://inspectapedia.com/plumbing/Air_Admittance_Studor_Vents.php

On 2019-08-14 by Russ

Thank you for your promt reply! I did as you suggested below.

First filling both sinks, removed the upper sink drain and using talc to see how the AAV was drawing in air

. I could not see the air being drawn into the AAV, nor could I hear it open. I closed the upper sink drain while still having water in it and removed the lower, repeating the process with the talc on the AAV. Same results with no air being drawn into it.

Then I removed all water from the upper sink and leaving drain open, pulled lower sink drain. The same results with the AAV and the talc. I removed the AAV and held it in the vertical position, gently drawing air by mouth, it does open and gentle blowing, it does close.

I went ahead and removed the extra 90 in the trap, I had that in to create space between the trap and the drain.

See also

PLUMBING DRAIN NOISES- how errors cause trap siphonage, odors, and noises

How to Test the Air Admittance Valve AAV

On 2019-08-14 by (mod) - How to test the Air Admittance Valve AAV - The Bag Test & the Talcum Powder Test

That extra loop trap seems unnecessary; if you shorten the sink tailpieces and raise up the Tee you can go to a single U trap that will improve drainage - but I note that's an independent issue from the slow venting with the Studor in place.

Some plumbers refer to this as a "positive pressure" problem; when water tries to run down the drain it's creating positive pressure in the drain system - that'll close or tend to close the air inlet at the AAV.

Sometimes the problem is that the water running down one side of the sink needs to push air up and out - the Studor or Air Admittance Valve (AAV) only lets air IN - it won't let air OUT.

So let's start by checking what's happening.

Close both sink drains, then fill both sinks, then with an accomplice listening or feeling or blowing talc at the Studor AAV, open one sink drain.

An alternative to blowing talc at the AAV while the fixture is draining, try simply securing a lightweight plastic bag over the AAV, holding it in place with a rubber band.

When you empty the fixture if the bag inflates we know there is a positive pressure problem at the drain - for which solutions will be given above.

If the bag over the AAV compresses or deflates then the AAV is drawing in air.

Try the same experiment with

- one sink drain (the smaller higher one) empty and its strainer removed.

Let me know what happens.

On 2019-08-14 by Russ - slow drainage problem after adding an AAV

I added a Studor Mini AAV to a double kitchen sink that has no other means of venting in hopes of improving the drain speed. After filling the sink and then releasing the water it still drains rather slow but does drain. If I remove the AAV it drains very fast.

There is a main vent line on the house for the toilets and shower but is 25' from the kitchen. If I pour dish soap in the drain with the AAV in place it does drain quickly. Any ideas on things to look at to improve the draining time on the sink would be appreciated.

This Q&A were posted originally at PLUMBING VENT FAQs-3