No plumbing vent...No problem

[cceccarelli]

Inspected a small old one bathroom house today. The drain lines were 100% re-plumbed professionally. The plumber did not install a plumbing stack vent but instead used an AAV only.

The question is, what is the down side of not having a vent, only an intake?

The plumbing fixtures worked fine and no signs of the traps getting siphoned.

Can there be a build-up of explosive gasses?

Will the gasses bubble up out of the toilet?

Is this the set-up for an urban legend where the person blows up while smoking on the toilet?

[Larry D. Kage]

Originally Posted by cceccarelli

The question is, what is the down side of not having a vent, only an intake?

You won't be able to clean out the wet vent from the roof with a hose.

[tnoisaw]

I do wonder if the AAV can handle the amount of fixture units that the house has.? I would think it would be considered a reduction in vent size. They also tend to be noisy.

[Bruce A. King]

AAV's are allowed but at least one stack through the roof is required.

[Jason A. Sieg, CMI]

From my understanding AAV's have been used all across Europe for hundreds (word used to show a long time) of years before they were even thought about being used here in America. They still have to be used properly. The down side to them is that they do have a life expectacne of, I think 75 - 100 years, then they need to be replaced. Just like the black rubber boots used to join PVC to Cast pipe.

The largest AAV's I have seen fit 1 1/2" or 2" PVC. That does limitthe # of fixtures one can have attached to a single AAV.

AAV's when working properly, although air to enter the plumbing when their is a vacuum in the system but, does not although gasses to escape. That is why we require at least one vent to exit through the roof.

Isn't it something that we need to pre-qualify everything we write on these boards or we will have everyone and their mother jumping all over us!

[dgagne1]

The aav may work but the house lacks a vent thru the roof. If there is a negative pressure on the sewer main for some reason it could fail causing a sluggish flush or slow drains. The VTR balences the house with the sewer. Will gas bubble up thru the toilet, no. Gases do not rise up thru the water that is the purpose of water in traps and the water in the toilet is the water in the trap. City manholes have holes in the sewer covers to prevent pressure build up and explosions. Septics should be designed to relieve pressure as well. I have seen 3" aav in places like church attics that have roofs with too great a pitch to accept a conventional roof flange but you still need to have a VTR at some point. If a roof penetration is impossible, some local municipalities allow side wall venting.Chances are this was not done by permit or inspected by the town. Was there a vent for the kitchen?
I would have noted the house lacks a vent thru the roof and the system should be looked at by a contractor.

[cceccarelli]

I did note the lack of a vent as a major defect along with many others this house had. Aside from code and all that, I was just curious as what the long term problem might be not having a vent and only an AAV.

I've seen several houses with aav's in the attic where the vent should have gone thru the roof. The plumbing all worked fine. I think it's a cop out to just quote code and not understand the reasons behind the code. I understand that sewer gas needs to be vented but what happens if it isn't and only aav's are in place? Anyone know?

Another example of code not cathing up to new methods is pex piping and requiring an air chamber on lines connected to mecanical valves (like dishwashers and washing machines). The manufacturers say pex doesn't require a water hammer damper because the pipe dampers the shock on it's own but we put one on anyways because code requires it.

[tnoisaw]

Just don’t forget that they are mechanical and mechanical things eventually fail. A vent through the roof may get clogged but this is rare. I doubt if the codes will ever allow just an AAV. As far as pex is concerned, depending on the location many codes are written for union protection, ie. California and copper, cast iron ec. They don’t want any materials that need little training to be approved because they are afraid it will effect the unions strong hold on the industry.