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Thread: how many fixtures on a 3" vent stack?

  1. #1
    General Engineering Contractor ballvalve's Avatar
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    Default how many fixtures on a 3" vent stack?

    1 washer
    2 sinks
    1 tub
    1 toilet

    Every plumber joe has a different idea. Can't reach the building inspector, he's always out to coffee.

    Seems to me they could all go on the 3" stack....

    Its a tough metal roof and I do not want a hundred holes in it.

    What do you real plumbers use as a figure?

  2. #2
    Forum Admin, Expert Plumber Terry's Avatar
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    In California, You can plumb a three bath home with one 3" vent.

    Most of the time, we would use

    2-2" vents, two or three bathroom sets and the laundry thrown in.
    1-1-1/2" vent Kitchen

    I have only used 3" vents on the West Coast on Condo and Commercial projects.
    On homes, I use the smaller vents.

    Most of the time, the kitchen is isolated so there isn't much else that can be added.

    A 2" line will vent three bathrooms, as long as there are other vents in the system to equal the "area" of one three inch vent.

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    Moderator & Master Plumber hj's Avatar
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    The number of vents through the roof, has LITTLE to do with the number of fixtures, and a LOT to do with where they are placed relative to each other, and whether the vents can be combined into a single penetration. The number of fixtures IS one determinant as to the SIZE of the penetration, however.

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    In the Trades Tom Sawyer's Avatar
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    Most codes are looking for one vent that is 1/2 the diameter of the building drain which in most cases would make that a 2" vent given a 4" drain. However, if you want to know how many fixtures can be served by a 3" stack you will need a copy of your state codebook because they are not all the same. I can tell you with certainty though that you will not exceed that on a residence.

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    Moderator & Master Plumber hj's Avatar
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    quote; Most codes are looking for one vent that is 1/2 the diameter of the building drain which in most cases would make that a 2" vent given a 4" drain

    Make that SOME codes. Others require the AREA of the vent to equal the incoming sewer which means FOUR 2" vents for a 4" sewer. Still others require a FULL SIZED pipe from the incoming sewer to the roof. And finally, in some cases after you determine the final size of the vent, it has to be INCREASED in size, (with the minimum size being 4" in many cases), as it passes through the roof to minimize rime frost closure.

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    In the Trades Tom Sawyer's Avatar
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    IPC and UPC which are the two most used codes are both one vent 1/2 the size, but HJ is correct, you need to know what your local code says. BV is in California which I believe is an IPC state for the most part. Obviously frost closure won't be an issue.

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    General Engineering Contractor ballvalve's Avatar
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    Looking at the mountains up a bit higher and there is still about 60" of snow to melt....

    OK, so 5 fixtures, with only one, the kitchen sink, 18 feet away, can tie into the 3" stack and go out the roof with just one pipe - right?

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    In the Trades Tom Sawyer's Avatar
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    If the kitchen sink is 18' away you are going to have to vent it individually and any other fixtures that are not within trap to vent distance

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    Forum Admin, Expert Plumber Terry's Avatar
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    UPC Code, California, Washington, Oregon

    Trap arm length.
    The distance from the p-trap to the vent.

    Table 10-1

    1.25" 30"
    1.5" 42"
    2.0" 60"
    3.0" 72"
    4.0" 120" unless it's a toilet vent, and then 72"

  10. #10
    General Engineering Contractor ballvalve's Avatar
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    The vent at the sink is very close, but the vent line run to the 3" stack is the 18'

    Seems like we should be using automatic vents like a mobile home anyway.

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    Forum Admin, Expert Plumber Terry's Avatar
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    Most all "auto" vents only work on negative pressure, not on positive pressure.
    They also fail and need replacement.

    If you have the walls open, I always prefer a vent through the roof, allowing both positive and negative pressure, that doesn't need repairs and they never overflow.

    I will use an AAV in a pinch. But they do have their limitations.

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    Moderator & Master Plumber hj's Avatar
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    quote; OK, so 5 fixtures, with only one, the kitchen sink, 18 feet away, can tie into the 3" stack and go out the roof with just one pipe

    Maybe, and maybe NOT. You are NOT telling us HOW the individual vents are getting into the attic so they can be tied together. HOW you do the piping is the important thing, NOT that the "sink is 18' away". That could mean MANY things, some of them legal and others not. It is like you saying, "My car can go 150 mph, is it okay if I drive it", without specifying if you mean on the road or at the track.

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    General Engineering Contractor ballvalve's Avatar
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    Well, the bright building inspector did not know the answer - he referred me to my mech. supplier. that guy says 18 +- fixtures on a 3" stack.

    Then he says the 18 feet to the stack is ok from the kitchen sink if its 2".

    Amazingly, this same inspector allowed the second story toilet to dump into the 3" vent from the downstairs toilet. [not my house, another copy]Never heard of wet vents I guess.

    I had to make the "plumber" cut out the run on mine. For my 5 or 6 future fixtures, he was going to put about 4 holes in my metal roof.

    I dont know about you guys, but when I see a house where it looks like it snowed vents on the roof, I see stupidity and future leaks.

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    Forum Admin, Expert Plumber Terry's Avatar
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    I'm a big fan of vertical.
    I like as many of my pipes to go straight up and down as possible.

    Popping vents through metal is a bit trickier though. Most of my vents are through comp shingles or cedar shakes.

    So.......your inspector never passed his state test? That's kind of sad.

  15. #15
    Moderator & Master Plumber hj's Avatar
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    quote; Then he says the 18 feet to the stack is ok from the kitchen sink if its 2".

    If it does NOT have an individual vent, then 18' is 12' too far. If it DOES have a vent within 6' of the trap, then you can go as far as you have to to reach the sewer connection. That is why we would have to know HOW you are routing the piping, before we can give an answer. Your plumbing inspector is completely useless and must be the brother of the mayor, because if he does NOT know what is permitted, how can he possibly tell if ANY installation is proper?

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