Why do I need vents? (How about AAVs?)

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talkingdog

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Hi,

First post here, from rainy Japan, where according to the code you can take your brand new $6000 Toto Neorest toilet and hook it up to an unvented plumbing system. I know, I know, our codes here are pretty backward, but I promise I'm not trolling here.

Venting is only required from the fourth story upward.

Now, here's the scenario. I'm specing out a 2 story house with three bathrooms, etc., and the plumber doesn't want to put in vents. In fact, I think he doesn't know how. He says the only advantage of venting would be that things flush faster.

Now, as a reader of this forum, I know that venting is considered essential from a health and hygiene point of view. And I could probably find a contractor to install a vent stack in this house.

But what about going with all-AAVs? My understanding is that you need one AAV for each drain, with an access hatch, and there is supposed to be one vent somewhere in the house, according to code (in the US, that is).

What is the practical reason for the requirement of at least one vent stack? Is there the possibility of some dire result if the house were to be all-AAV with no stack at all?
 
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Jimbo

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Your plumbing system may be vastly different. I do not know.

In the US, every plumging fixture has a trap, to seal out sewer gas from entering the house. Sinks, tubs, showers, the trap is right under the fixture. On toilets, the trap is internal to the china bowl.

Vents have nothing to do with draining, since an open sink or tub drain, or toilet, vents itself. What the vent does is prevent the trap from being siphoned dry when water and waste from other fixtures passes by that connection.

Air admittance valves provide the venting function, with some limitations. First, they are mechanical and thus subject to eventual failure. Second, they prevent negative pressure in the drain, but do not prevent a positive pressure, so they cannot be used as the only vent in a total house system. In some areas, the codes allow them . In some areas their use is limited or prohibited.
 

Geniescience

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What Jimbo said is all good.

It is also true that with vents things flush faster, because air in the pipes has a place to escape to, so draining water can start moving sooner. Otherwise, water pushing to start draining has to blow all that air out first. Air is not compressible (unless under high pressure) so it has to displaced when water flow increases.

What are the pipe diameter sizes in Japan?

david
 

talkingdog

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Sizes are all metric, so the numbers won't make sense, but I think they roughly map to about the same sizes you will see in the US.

It looks like there is normally a P-trap inside the house and then another trap outside in the ground.
 

talkingdog

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Here's a diagram of the way it usually works, with the outside traps. For toilets on the second floor, the plumbing is often run right out the exterior wall and down outside. (supposed to make maintenance easier).
 
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Geniescience

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metric size is OK

anybody can convert metric to "imperial" sizes. Please tell. Metric is OK.

The diagram doesn't show the shape of the fittings at the join points where pipes get connected. Do you know what shape the fittings are?

david
 

talkingdog

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Gee, I'm a little embarrassed to admit it, but whenever I have to do some plumbing, I usually go to the home center and rummage around in the bins until I see what I need. On my house there are two sizes for water supply, 12 and 20, and the waste pipes are 40 and 50. Part of the graywater lines are 50 mm clay tile. There's no soil stack since we have the old-fashioned type of toilet (and I mean really old-fashioned!)

In the new house I we are going to have the latest thing, what they are calling "system plumbing," though, including home run plumbing for the water supply, and also I guess what you could call home run plumbing for the waste lines, with flexible pipe feeding into a central header.

559806746_d82cb5c67b.jpg


http://www.flickr.com/photo_zoom.gne?id=559806746&size=o
 

Geniescience

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cylindrical connection thingies

12mm and 20mm are 1/2" and 3/4" for all intents and purposes.
40mm and 50mm are close enough to 1-1/2" and 2" to work under the same principles, since a 50mm diameter pipe has 150% the capacity of a 40mm diameter pipe.

Those cylindrical connection thingies are what I've never seen.

I see P traps (that can act as S traps when large volumes of water go downhill in unvented drains) but not under the tub and not I guess in the wall box above the (iguess) washing machine. So maybe the tub has a drum trap or bottel trap under it. And the washing machine has an air break in its wall device.

eplumbingo skideska?

David
 
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talkingdog

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Those things outside are also traps, I believe, as the lids are flush with the surface of the ground. Is this the same thing as a "double trap"--and if not, what is a double trap?

That header device into which all the green lines are feeding is supposed to have backflow dampers in each chamber, and also a lid for cleanout (which is one of the merits of this system. Another merit is that the whole houseful of plumbing parts comes precut and numbered in a box, based on their design from your CAD drawings, and it takes no more than a day for a screwdriver monkey to put it all together for the one house)
 

talkingdog

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>>eplumbingo skideska

That's pretty good ersatz Japanese. Not sure how you would say that. Maybe they would say "haikan kouji no koto" for plumbing.

Now, as for me, I like plumbing plenty--except I don't like clearing my stopped up drain lines of giant bamboo runners, like I had to do this spring. Ain't nothin ornerier than a mess of bamboo runners.
 

Terry

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dwv_b2.jpg


This is USA plumbing above

The pictures you have of the Japanese plumbing is pretty cool.
I would have never even considered that they would do things that way.
 

GrumpyPlumber

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talkingdog said:
What is the practical reason for the requirement of at least one vent stack? Is there the possibility of some dire result if the house were to be all-AAV with no stack at all?

I'm guessing "AAV" is mechanical vent...or Studor vent.
They're legal in some states, but not most.
It's an ongoing debate over reliability, and plumbing boards are hard to change when it comes to time tested methods (i.e. what if the mechanical vent inside a wall fails...as opposed to a regular vent...no working parts, no potential mechanical failure).
The whole venting system in a house is set up to allow for the vacuums created when fixtures drain to not suck the water from traps....try this...go down to your basement and open an end cleanout...have someone flush a toilet and keep your hand over the cleanout (cleanout thingy).
You quickly understand why vents are needed...imagine a kitchen sink draining while one..or two people flush toilets simultaniously...there goes the trap weir in you bathroom lav...then the next morning the house smells like a college dormitory after spring break.
 

talkingdog

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Thanks, that's a very helpful explanation of the mechanism.

I have to chuckle at your request, since the only traps in my current house, with its prewar plumbing, are outside in the ground. When i first moved in here I did a doubletake, "Hey where are the traps and vents?"

Ok, so back to the new house, which is going to have modern plumbing. Normally in Japanese residences all the plumbing is on the ground floor--so would lacking second floor plumbing or a basement minimize the risk of the trap water getting sucked out as you describe, and thus allow them to get away with no vent requirement in their code, as a practical matter? Or, as I suspect, is the idea totally bogus?

Next, I have a ballpark bid on the plumbing with three powder rooms, one full bath and one kitchen at $15K--with no vent system. If I were to stipulate that they build a vent system to accommodate the above zones, how much more money am I probably talking? Or put another way, how much of the cost of a plumbing bid is made up of the vents?
 

Terry

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I would have no idea as to whether they would even know what one is then.

The vents don't take very much time. Pipe and fittings are not very much of the cost. It's mainly the labor. And it's not really very much for that either.
 
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GrumpyPlumber

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I'd strongly suggest venting...even mechanical over nothing at all.

It shouldn't add much at all to the price...especially if they can use mechanical.

I'd rather not have to wake up to a beautiful new home and the smell of sewage, wishing I had.
 

talkingdog

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>The pictures you have of the Japanese plumbing is pretty cool.

Here are some more pictures fer ya, these are from Toto's "Aqua Highway System" (my architect says this stuff is a bit pricey, but I bet one makes some of that back on the labor costs):

First, the visualization of the new system with the flex pipe, header and single outdoor trap:

hai_a_02.gif


Now here's the header in see-thru:

hai_b_02.jpg


Next the flexible sleeve elbow for foundation exit:

hai_c_02.jpg


Exiting the slab:

hai_c_04.gif
 

talkingdog

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More Toto plumbing ****:

Here's their PEX "water control unit" manifold:

lin_b_08.jpg


Anti-freeze PEX (with heat assist for cold climates:

lin_d_12.gif


Quick release water socket for toilet with instant safety shutoff:

kik_a_02.jpg


Inspectable elbow with cam-shaped escutcheon (I like this one)

kik_a_13.jpg
 

Terry

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Wow,
Without seeing how the connections are at the fixtures, it would be hard to say.
Everything about that is so different from what we do in the US.
If they are using oversized pipe, it may allow for some venting.
I think here they would call something like that a circuit vent.
I did that for some drains in a meat market where I could not run vents up where the coolers were. I oversized the p-traps and the line connecting them.
The idea being that the water only gets so high in the pipe, and there is always air above the flow line.
Much of our piping systems are really sized for the minimum allowed.
I guess the question is, When you go into homes plumbed that way, do you notice smells from the plumbing?

When I was last in Guatemala, there was some plumbing for the kitchen sink that smelled very bad. I did what I could without going into the brick wall, replaced the p-trap and other parts, but the smell came back.
I couldn't see how it had been plumbed inside the wall.
By the way, I was on vacation, not working. I could go home and forget about it.
Well not really, I'm telling you this, so it's still there in the back of my mind.
I think you will need to ask those questions there in Japan. Ask their experts what they think.
But you do have me intrigued. Now I want to go there and see some of this.
 
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