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Thread: Stack Venting

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  1. #1
    DIY Junior Member sfphoenix75's Avatar
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    Jan 2007
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    Norwood, MA
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    Default Stack Venting

    Hello gentlemen,

    I am doing a second floor bathroom remodel and have hired the help of a plumber. He repiped the DWV system in the bathroom, but I'm not sure if it was done properly.

    I have a 4" main stack. A 3" toilet drain is tied into it 15" away. The toilet drain has a Y branch off it that runs 5 feet of 1 1/2" PVC.

    On this branch is a Y to the lav P trap, a second Y to a 1 1/2" vent pipe, and then it terminates with another P trap for the tub. Total run is 5' from toilet drain or 5.5' from main stack. (see illustration below)

    I have read that sometimes second floor bathroom groups can all run off a single branch into an oversized stack vent without individual venting. The plumber told me that he only added the vent pipe in between the lav and the tub for additional air to the system and that I didn't really even need.

    Will this work? Should I be concerned about siphoning the P traps?



    4" main
    |
    |
    |
    |
    | lav P trap 1.5" vent (to roof)
    |\ ___/________/______P trap for tub
    | \ /
    | \_3" toilet drain off main stack with 1 1/2" Y branch running off it (above)
    |
    |
    |
    Last edited by sfphoenix75; 03-06-2008 at 11:38 AM.

  2. #2
    Plumber canton's Avatar
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    Jul 2005
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    Massachusetts
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    Default I don't think so.

    In Ma. 3 requirements for Stack venting.
    1.fixtures connect independently into the drain
    2. Are on the same floor
    3.1/4" pitch per ft.
    Maximum distance from trap to vent for the following sizes:
    1 1/2" - 5'
    2" -6'
    3" -8'
    4" -10'
    I also believe that you're going to have to find some way to vent the 1st floor bathroom now that your venting the 2nd through the stack.

  3. #3
    DIY Junior Member sfphoenix75's Avatar
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    Default

    That requirement that they all connect independently into the stack is the primary issue I guess.

    The circuit vent he added on the branch goes to the roof. I wonder whether this will compensate.

    Any ideas whether his setup will provide adequate venting? If not, how would you improve the system without completely redoing it?

  4. #4
    Plumber patrick88's Avatar
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    Sep 2007
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    Webster Ma.
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    Default

    Your 2nd floor bathroom will not have drain or vent problems. That is till you clog your fixtures from normal use.

    Like Canton said you will need to run a vent for your 1st floor fixtures.
    I'm just starting to work with an old friend of mine to bring solar electric and hot water systems, wind turbines, Flex Fuel Boilers, batteries, hydroponic gardening, books, pellet grills and more. Also the parts for DIY installation.

  5. #5
    Moderator & Master Plumber hj's Avatar
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    Aug 2004
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    Cave Creek, Arizona
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    25,638

    Default vents

    How the pipe is run dictates whether it needs additional vents or not, not necessarily how far it is to any other vent. And by connecting it to the "vent" for the lower bathroom he has technically negated its use as that bathroom's vent.

  6. #6
    DIY Junior Member sfphoenix75's Avatar
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    Jan 2007
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    Norwood, MA
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    Default

    Thanks for the advice guys. I appreaciate it!

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