Trying to decide if I need AAV for my sinks
derekr
| Posted in General Questions on
my plumbing is vented out my roof and I have a sceptic tank
my drain lines are coming out of the floor from the crawl space for my sinks
I cant use S trap since they are banned so do I use a P trap connected to a Tee with AAV on top? Or do I connect the P trap to a 90 degree that goes down to my floor with no aav
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You need a p-trap that goes into a tee. The down end of the tee goes to the drain line, the up end has to go either to a vent that goes through the roof or an AAV. The tee has to be within six feet of the trap for 1-1/2" pipe and eight feet for 2" pipe.
You can bury the tee in a wall but the AAV has to be accessible, they fail and when they do they stink up the house. If the sink is in a cabinet you can put it in the cabinet.
All P traps need a vent connection. Typically this is simply another line that runs to your stack from the P trap. So you have one line that is the drain down to the crawl, the other up to the attic and to the stack).
You can use an AAV but usually best to avoid these in a new build. Kitchen island sink is about the only AAV you should have but even that can be vented without one.
So I would have to run a whole other pipe to my vent from the tee or just use the aav, seems easier to just use the aav
If all 3 sinks already have a pipe going to the vent in the crawl space then I wouldn’t need the aav? Or does the vent have to be above the trap
Also all these drains are in the floor and going into a cabinet none are in the wall so running another pipe to vent would make that more complicated as well
My bathroom sink drains are coming out of the floor so it’s like I have 3 islands in the house
Vent has to be above the trap. This is true for every plumbing fixture in the house.
And the vent going out my roof doesn’t count as vent being above the trap even if my sinks are connected to vent in the crawl space?
It needs to connect to the vent above the trap.
It's sometimes possible to do a "wet vent", but that depends on the rest of the pipe layout. I wouldn't assume that to be the case here, so your existing vent(s) in the crawlspace aren't going to work for your sinks here.
AAVs are great for renovations where you are stuck, but should be avoided in new construction. AAVs are a failure point, and aren't really optimal regardless. Ideally you want to run a vent line from the upper part of your tee up into the attic, then either out the roof or into a larger common vent. You can usually run multiple vents to a single roof vent and end up with a sort of mirror image of your drain system (kind of, not exactly) up in the attic.
It's difficult to really give you an idea how to solve this issue without seeing the rest of the plumbing layout.
Bill
Yea that’s not possible for me because I don’t have an attic in these areas it’s all cathedral ceilings so I may no choice but an AV for the sinks
I wonder if an S trap would be better even if I’m not supposed to use it over a P and aav because I definitely don’t like having things that can fail
Derek,
Isn't this new construction? How did you end up with no vents for the sinks?
Changing the type of trap doesn't mean you don't have to use a vent or AAV. You need those whatever you do. There may be a work-around if your code allows loop-vents or wet venting, but you need a plumber involved here. Doing this work is beyond your skill set.
S traps are prohibited now I think just about everywhere. They can allow for the trap's water "plug" to be siphoned out. They're bad news and you shouldn't use them. They are NOT a solution for your problem here.
You could potentially run a vent up through the wall and out the roof right above the wall. That's probably not ideal, but may be your only option here. AAVs should be a sort of last resort. On a new project, you really shouldn't be needing AAVs anywhere, except -- maybe -- in a sink on a kitchen island. Even then, there are better ways to do the venting.
I agree with Malcolm here. Get a plumber involved, so that you can lean on the plumber's experience and find a vent solution that will work in your specific situation.
Bill
Aav work fine. Everything in a house is a failure point even a vent through your roof. If you buy a nice stud or aav you most likely won’t have to replace it for 20-30 years and when you do you just unscrew it. Just put a T right behind your p trap and make sure the aav if 4” above the horizontal drain. Or if it is not in a cabinet run it up in wall to access panel.
Aav work fine, and if you get a bum one to start they are incredibly easy to replace.
freyr-design,
Our code is quite restrictive a to where you can use AAVs.
"Air Admittance Valves
1) Air admittance valves shall only be used to vent
a) fixtures located in island counters,
b) fixtures that may be affected by frost closure of the vent due to local climatic conditions,
c) fixtures in one- and two-family dwellings undergoing renovation, or
d) installations where connection to a vent may not be practical."
The IPC does not have those restrictions.
https://www.iccsafe.org/building-safety-journal/bsj-technical/codenotes-installation-of-air-admittance-valves/
I don’t think those restriction are based on anything practical but instead on unfounded fear of a mechanical device.
Deleted
freyr_design,
I think it comes from a philosophical starting point of keeping the venting as passive as possible for longevity. Whether that still makes sense now with all the other mechanical devices that have crept into plumbing systems I don't know.
For better or worse, I've always used loop-vents for kitchen islands.
Ya I suppose my point is vent penetrations are at least as risky, between frost, snow, rubber boot failures, I feel like aav are honestly probably less risky than passive vents, and much easier to replace.
I’m A and D
For A, put an AAV under the counter and don't look back.
D is a little more subjective. If the sink is on a wall the vent can go through the wall, it can go around the house and up and down and finally connect.
And if it's not on a wall -- or on a wall that doesn't connect to other walls -- it can be treated like an island.
AAV for all 3 sinks it is then
Because the bathroom sinks are set up like islands even though they are against the wall
Derek,
That we are talking about vents on a kitchen island changes the whole question. I wish we had known that from the start.
d) Can only be used if the plumbing inspector approves it.
I paid the plumber to do the rough in, then I was going to connect the fixtures and sinks, I know how to do it it’s easy enough I just want to make sure I’m buying the right parts
This is a reply to one of your other posts but it wouldn’t let me reply to it
The purpose of the trap is to seal the drain pipe to keep sewer gas out of your house, it stinks and has various health and safety issues. Water flowing in a closed pipe can create a vacuum which can drain the trap and defeat its purpose. The purpose of the vent it to prevent a vacuum from forming in the drain to protect the trap from getting sucked out.
In order for the vent to work properly there has to be a continuous layer of air from the vent to the top of the trap. In order to maintain a continuous layer of air the vent entrance can't be any lower than the diameter of the drain pipe below the trap. Properly installed drain pipes slope at exactly 1/4" per foot, so a drain pipe will fall 1-1/2" in six feet. If you have a 1-1/2" drain pipe the vent entrance has to be within six feet of the trap in order to maintain a continuous layer of air along the top of the pipe.
The vent system is basically a mirror image of the drain system. Each fixture that has a drain has a vent. The drains all come together and exit the house through the basement, the vents all come together and exit the house through the roof.
Seems to me you are trying to avoid putting another vent in your roof.
Every fixture needs a vent you can interconnect them and have fewer roof penetrations.
Getting a good vent in an island is difficult at best but possible. If your code allows admittance valves that make islands much easier to install but become a problem later every time there is a problem with that fixture mostly wrongly the air valve gets declared to be at fault.
Walta
Yea I’m not putting any more holes in my roof so I’m going with AAV
Drywall is up, shingles are up etc not happening
I think this is what my plumber did, all of plumbing is very close together within like 8-10 feet and he connected them all to 1 vent, my 2nd story bathroom is directly above my first floor bath and then the kitchen is just on the other side of the wall of my first floor bath, but it sounds like my trap still needs its own vent?
Every fixture needs a vent. It's not really right to say it's "its own vent" because normally they all tie together and go through the roof.
How many sinks are we talking about? Are they all island sinks? In post #16 you said "A and D," but are some sinks A (island) and some D ("not practical") or are they both island and not practical?
Because I don't think any plumbing inspector is going to think that having to redo drywall is an insurmountable barrier. It happens all the time during the construction process.
3 sinks = 1 island and 2 bathroom sinks, yea the plumber told me that all of plumbing was so close together that he was able to connect everything to 1 vent
But I’ll still need the aav for my p traps?
Do the drains for the bathrooms go into the wall or into the floor? If they go into the wall I'd be astonished if they aren't already vented. If they go into the floor, that's kind of weird and an AAV is going to be needed.
For the island, put an AAV in the cabinet under the sink but above the trap and don't look back.
The plumbing starts in my crawl space, comes up through the floor to the first floor, then goes up wall and comes out of the floor on the second floor, then the vent goes out the roof above the second floor
If I didn’t need the aav would it hurt to have it?
The normal way to plumb a bathroom sink is that the drain pipe comes up through the floor inside the wall. About 18" above the floor there is a tee, with one end facing up, one end facing down and one end facing out. The end facing out goes to the trap and from there to the sink. The end facing down goes to the drain, and the end facing up goes to the vent.
Usually the plumber will install the tee and a stub facing out, then the drywall guy comes and covers everything up, then the plumber comes back and hooks up the trap and sink onto the stub.
Does this describe what you have? If so, you're all set, just connect your trap and sink and enjoy.
derek,
I don't mean to be rude, but it's increasingly obvious that you don't have the faintest idea what you are doing. You need to get your plumber back.
No tees inside the walls from what I remember before the drywall went up
None of my drains come out of the wall
Did the plumber leave a stub of any kind in the bathroom for the sink drain? If so, where is it?
Yea it’s coming out of the floor if your talking about the pvc drain pipe, same for hot and cold lines
How are the toilets and tub/showers vented? When the fixtures are all against one wall, there is typically a vertical vent pipe in the wall behind the toilet, with the sink and tub/shower vents tying into that.
Everything is connected to 1 vent then it goes out the roof
I need to go in my crawl space to look but I wonder if it’s something like this? If the trap is below my floor would I even need a trap directly at the sink?
All the sinks could be connected to vent in this way in the crawl space
The trap can be up to 24" below the drain. That's measured from the rim of the drain in the sink to the water level in the trap. The trap could be below the floor like that but it would have to be a deep and low sink.
If it’s connected to the vent this way then I still need the aav then
You know, I don't know. The piece between the sink and the trap is called a tailpiece, I don't know what the remedy is for a tailpiece that's too long. It's not going to be adding an AAV, which needs to be on the downstream side of the trap.
Probably the remedy is moving the trap up and adding an AAV. Or, if the vent goes through the wall behind the sink, tying into the vent in the wall.
The reason for the height restriction on the tailpiece is that if water leaving the sink gets going too fast it can sweep the water out of the trap. An AAV isn't going to help with that because it's not caused by a vacuum in the pipe.
I did some reading over on the Terry Love plumbing forums about this, because I was curious. There is a 24" max tailpiece length, but no minimum. Excessively long tailpieces can be dealt with by using some 45s or 90s to break up the total length of the tailpiece so that the vertical part before the trap isn't excessively long. There are some pics in this thread: https://terrylove.com/forums/index.php?threads/long-tailpiece-remedy-vanity-drain-configuration.49241/
showing what was done.
It's not elegant or ideal, but sometimes may be the only option to deal with the problem.
Bill
K I’m just going to do the AAV’s theres just 1 thing I want to be sure of though, if these sinks are correctly vented some where that I can’t see would the AAV cause harm or would it just be there and not do anything?
I’m guessing if they are vented then the aav would just sit there and never open or close and would be safe to install even if I didn’t need it
The AAV only opens when there is a negative pressure in the pipe. That's what makes it an Air ADMITTANCE Valve: it selectively lets air INTO the pipe when needed. It operates like a check valve, preventing anything from getting out. If the pipe is properly vented, the AAV should not operate, or, if it does, it's just providing more air coming in when water is going down the drain (in which case you probably have a plugged up plumbing vent somewhere).
I don't see a functional issue with adding an AAV where a vent already exists, but I'm not sure if that's a code issue. You're probably OK with the code too, but it's not something I've ever really looked into as you wouldn't normally put in a double vent arrangement intentionally, which is basically what you're asking about here.
Bill
Code is pretty slack here so the safest thing would be to use them even if I don’t need them, and if do need them then they will be there anyway
AAV's tend to fail over time and when they do they leak. Which means allowing sewer gas into the house. I wouldn't put one in unless you were sure it was necessary.
If the sinks are vented properly then the aav should never open or close which means there’s no way for it to fail
They also could always be removed and just put a cap on top of the tee if they weren’t needed
And if they are needed then I need them anyway
Don’t see any downsides
Actually I could put the cap on now to see how it drains if it doesn’t drain well then I’ll remove the cap and put on the aav
> "Actually I could put the cap on now to see how it drains if it doesn’t drain well then I’ll remove the cap and put on the aav"
Vents aren't so much about making things "drain well" as they are about keeping a slug of water in the trap to prevent sewer gas from getting into the house. You aren't going to be able to easily tell if the vent/AAV is working or not based just on the sink "draining well". Sometimes a clogged vent will result in excessive gurgling noise, but not always. I wouldn't rely on subjective testing here, you need to make sure there is enough water in the trap to completely block the pipe AFTER you're done running stuff down the drain. You should still do things properly in terms of venting though, regardless of how the drain appears to operate.
Trust me: stuff can always find a way to break.
Bill
K I’ll just go straight to aav then so I’ll have all bases covered
"If the sinks are vented properly then the aav should never open or close which means there’s no way for it to fail."
No, they just fail from time.
If they are always closed what would make them fail
If it did fail from time only and not by opening and closing it would be a very long time at which point I would just replace it in 1 min