# AAV on Washer? pls comment on design



## Queso Bandit (Mar 17, 2009)

The washer is about 6ft from the stack so I'm thinking it should have it's own vent (especially since horizontal drain is shared with the laundry sink). 

Could the pump from the washer siphon the sink too or do you think the 2" drain to the stack is adequate for sink venting?

Any preferred way to connect washer to sink to stack? I have wall/attic constrictions to prevent a standard vent on the washer.

Thanks


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## TheEplumber (Jul 20, 2010)

I am not a fan of AAV's but if I were to use it on your layout- it would be on the outlet side of the laundry sink to eliminate the s trap. It would then be venting both fixtures.
The vertical pipe to the sink would be 2" with 1.5" trap


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## Javiles (Dec 12, 2011)

couple problems with your set up as E mentioned that S trap has to go also aav's are for negative pressure not positive, depending on your code you cant have a mechanical discharge on the same waste arm as a gravity feed discharge even though well vented it could still pull your trap dry, recommend either 3 inch line to the machine or 2 - 2 inch independent arms. you mentioned attac..?? is this set up in the attic, and if so what line are you connecting too hopefully not a vent stack??


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## hammerlane (Oct 6, 2011)

Stack the San-Ts on the stack if you have room. Keep the washer San-T below the sink San-T since the washing machine pumps a lot of water fast. You dont want a "major" over a "minor"

Below #7 is for the laundry sink.


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## Queso Bandit (Mar 17, 2009)

Thanks for the replies.

I was hoping to avoid a 3" line or (2) 2" lines since they are running through the inside of cabinets. Just to save space really.
Hmm...Could positive pressure generated from the pump pull the trap dry if it is vented?
If so, 2 separate pipes makes sense.

I know to avoid s-traps, but just out of curiosity, is it still an s-trap if the horizontal length just beyond the trap is 2x the diameter of the pipe?

Javiles- I'm connecting to a 4" stack that serves as as the main drain for a toilet and lav (vented independently) but also the tub (which will now be wet vented with the new connections in the 4" stack).


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## Ghostmaker (Mar 2, 2013)

Do you want to do it correctly or just hack it in and lower your resale value later?

You will have to vent to something that is not a drain on the floor above.


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## Queso Bandit (Mar 17, 2009)

The code is unclear about AAVs with washers.
I'm not hacking anything in, it is single story without anything above on the vent stack.

At this point I guess my options are an AAV on the sink as Eplumber mentioned or separate lines (3" for the washer and 2" line for the sink) to the stack.


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## Javiles (Dec 12, 2011)

Queso Bandit said:


> The code is unclear about AAVs with washers.
> I'm not hacking anything in, it is single story without anything above on the vent stack.
> 
> At this point I guess my options are an AAV on the sink as Eplumber mentioned or separate lines (3" for the washer and 2" line for the sink) to the stack.


There are gray areas in the code book but this where experience and knowledge of how a drainage system works is important , for example AAV are valves that open when the line requires air for this to happen the water traveling through the line must create a vacuum, the only problem is that all plumbing systems work on positive and negative values, so the location of a AAV and the line that its servicing must be in a configuration that allows only negative pull on the AAV if not what happens is that the rushing water hits an air dam and forces the water back through the washer stand pipe, thus a gush of water on the floor. this is until there is a balance in the line then will continue to drain. remember on a washer branch your dealing with a pump discharge which then converts to gravity flow, AAV's should not be used on a washer vent. you may have a better luck by self venting the line which is now illegal under most codes.


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