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Thread: venting a shower with an AAV

  1. #1
    DIY Member pronouncedeyen's Avatar
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    Default venting a shower with an AAV

    I'm plumbing a new bathroom in an old house. A really old house. And since it's made of brick and plaster I decided to vent using AAVs instead of tearing up plaster walls and ceilings to get to the stack.

    I'm getting ready to tie the shower drain into the main 2" branch that the bathtub and sinks connect to. The shower drain is about 2 feet away from the wall where the AAV will go and 2' in the other direction from the DWV branch.

    I'm considering 2 ways to plumb it.

    Name:  shower2.GIF
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Size:  2.7 KB This way is obviously simpler but I believe that's what is called a wet vent which I guess is frowned upon.

    Name:  shower1.GIF
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Size:  2.6 KB I believe this way is a "dry" vent but to me seems like it would have less flow since it's 4' more pipe and has 2 more turns in it.

    I'm obviously a DIYer but I do want to do this the right way. Thanks all!

  2. #2
    DIY Senior Member asktom's Avatar
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    Do it the second way, drainwise. The first way is an "S" trap that can siphon. I'll leave the AAV for others to comment on.

  3. #3
    Moderator & Master Plumber hj's Avatar
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    Do it the first way and you do not need the AAV because it will be ineffective and illegal. How do you intend to provide access to the AAV, and it does need a source of air.
    Licensed residential and commercial plumber

  4. #4
    DIY Member pronouncedeyen's Avatar
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    Quote Originally Posted by hj View Post
    Do it the first way and you do not need the AAV because it will be ineffective and illegal. How do you intend to provide access to the AAV, and it does need a source of air.
    Why is it illegal? I thought AAV's are approved in my area. Or maybe not for a shower? I'm not sure. If I do it the first way without the AAV then the shower won't be vented. Is that ok?

    I was planning to have access to the AAV from the other side of the shower wall which is in a laundry room. And are you saying that the inside of the wall doesn't provide enough air flow for the AAV?

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    Forum Admin, Expert Plumber Terry's Avatar
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    are you saying that the inside of the wall doesn't provide enough air flow for the AAV?
    Yes, that's why they make boxes with open air grills for them.
    And they fail, so replacement will happen at a latter time. You don't want to bury a part that needs replacement.

  6. #6
    DIY Member pronouncedeyen's Avatar
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    Thanks guys. I'll put the AAV behind an air grill. So then should I go with option #1? or #2? Does it not make a difference? Which will have better flow?

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    DIY Senior Member asktom's Avatar
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    #2. The purpose of the vent or AAV is to prevent the trap from siphoning. In #1 you have created a siphon before the AAV comes into play, so it does nothing. If the trap siphons and breaks the seal there is nothing between your nose and whatever is in the sewer. You need to use plan #2.

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    Moderator & Master Plumber hj's Avatar
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    If you used plan #1, you could put a hundred AAVs in the wall and they would do NOTHING to prevent siphonage.
    Licensed residential and commercial plumber

  9. #9
    DIY Member pronouncedeyen's Avatar
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    OK, thanks again all. Is there a certain height the AAV should be above the shower floor? I've heard differing opinions on this.

  10. #10
    Nuclear Engineer nukeman's Avatar
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    You may have other options. You say it is a 2" line that the tub/lav connects to. You should take a pic or make a drawing of the layout. If the lav is 2" and if that line is within 5'-8' (depending on code) of the shower trap, you could wet vent the shower by connecting the drain into the lav drain. This way, you wouldn't need to mess with the AAV.

  11. #11
    DIY Member pronouncedeyen's Avatar
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    it's not all 2". I'll make another drawing.

  12. #12
    DIY Member pronouncedeyen's Avatar
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    Name:  bath-laundry-plumbing.jpg
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    OK, here's the layout. The red pipes are 1.5", the blue pipes are 2", and the brown pipe is 4". Get it? Brown? You guys probably never get tired of toilet jokes, right?

    Now I'm not at home so all distances are approximate but they're probably within 6 inches or so.

    The sinks (lavs?) have P traps that meet up with PVC behind the wall. I put AAVs on both sinks because the PVC goes straight down and meets up under the floor. Maybe that was overkill. The shower is about 11' from the first sink so I figured I needed another AAV for that. I'm not planning to put an AAV on the bathtub because the wall I'd have to put it in is concrete. I guess I could put one out in the open but I figured I'd just deal with a slow running bath for the 3 times a year my wife actually uses it!

    So, can I use the sink's AAV to vent the shower? Or is it too far away?

  13. #13
    Moderator & Master Plumber hj's Avatar
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    AAVs, have NOTHING to do with how fast the tub drains, unless you already have another problem with the drain system. If anything, they will keep it from draining TOO quickly and creating siphonage. WHERE you need vents, or AAVs, has as much to do with what is flowing past the connection as it does distance. I would put it in.
    Licensed residential and commercial plumber

  14. #14
    In the Trades Tom Sawyer's Avatar
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    Where's the tub vent? And are you seriously going to use 3 AAV's on a single bathroom? If you knew what you were doing you probably wouldn't use any or at worst only one.
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

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    DIY Member pronouncedeyen's Avatar
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    Quote Originally Posted by Tom Sawyer View Post
    Where's the tub vent? And are you seriously going to use 3 AAV's on a single bathroom? If you knew what you were doing you probably wouldn't use any or at worst only one.
    Well, I don't know what I'm doing! That's why I'm on this forum in the first place.

    We're using AAVs because the house is 100 years old, made of brick and plaster and the closest vent is 25 feet away from the farthest sink. I suppose you're right - that I could have had the drains for the sinks meet behind the wall and just use 1 AAV but again - I was trying to minimize how much wall I tore up. So I chose to connect them under the floor because the ceiling underneath was open. And because they both met underneath I had to run an AAV for each sink.

    I'll go ahead and put in another AAV for the shower. Seems like the least bad choice.

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