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

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  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.

  3. #3
    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.

  5. #5
    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.

  6. #6
    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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