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Thread: Vent Stack vs. Stack Vent

  1. #1
    DIY Junior Member CTWeekendWarrior's Avatar
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    Default Vent Stack vs. Stack Vent

    What is the difference between a Vent Stack and a Stack Vent?

  2. #2
    Moderator & Master Plumber hj's Avatar
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    Default simple

    A vent stack is a vertical pipe parallel to the waste/soil stack to which each floor's vents are connected. The stack vent is the final portion of the waste/soil stack above the highest fixture.

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    DIY Junior Member CTWeekendWarrior's Avatar
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    Default The next question

    In my house, I only have one vertical pipe that exits the building. Based on your reply I would say that makes my pipe a stack vent.

    A follow up question: If this is the only vent, any additional plumbing that I install would require a new vent stack, or is it acceptable to tie new vents into the stack vent?

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Default

    Depends on the diameter of the pipe and what you have and what you are adding...there is a minimum size per fixture units present requirement. Where you can tap in is also determined by codes.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  5. #5
    Moderator & Master Plumber hj's Avatar
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    Default vent

    Normally a vent stack is only required in multistory buildings and it could connect back to the stack vent at the topmost floor or exit the roof separately. Most residences only need the stack vent, occassionally two story buildings may need a "vent stack" to connect the lower fixtures to the upper floor's stack vent.

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    DIY Junior Member CTWeekendWarrior's Avatar
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    Default

    Well let's get to the heart of the matter. I live in a cape style house with one bathroom on the first level. The drain lines from the WC and tub on the first floor go to the basement and connect to the stack. This stack extends up through the roof. (See first pic).



    I am in the process of adding an additional bath on the second floor. I am assuming that I cannot drain the WC into the stack vent on the second floor, but I would like to drain my double lavatories into the stack vent. Is it ok to add a drain line to this stack vent, assuming that my first floor fixtures most likely vent into the stack vent at an elevation below my new lavatory drain? Is it ok to add new vent lines to this stack from the new fixtures in the 2nd floor bathroom?
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    DIY Senior Member construct30's Avatar
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    Default

    Does the low heel 90 go up to a badly leaking toilet or what? I would fix the leaking toilet and the low heel 90 shouldn't be there. It would be a T on it's back and you shouldn't put a vent or drain off the back side of a toilet like that. No, you can not wet vent between floors and if you turn a vent pipe into a drain that is what you would be doing, I think if there are any vents coming into it from the floor below under where you would put the new drain. All the vents from the first floor have to be above the water level. IRC

    The tee can only be used this way
    Last edited by Terry; 12-26-2008 at 12:33 PM.

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    Commercial Plumber markts30's Avatar
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    Default

    Just a couple of concerns...
    Is the grey pipe SCH80 pvc?
    PVC and ABS tend not to glue together very well...
    Seems like you have many transitions in your piping...

  9. #9
    DIY Senior Member construct30's Avatar
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    Default

    Quote Originally Posted by markts30 View Post
    Just a couple of concerns...
    Is the grey pipe SCH80 pvc?
    PVC and ABS tend not to glue together very well...
    Seems like you have many transitions in your piping...
    IRC says you can not glue different types of plastic pipe for that reason.

  10. #10
    Moderator & Master Plumber hj's Avatar
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    Default vents

    Technically vent lines can tie together anywhere desired as long as the sizes correspond to the fixture loads. Legally, you cannot connect fixtures on one floor to the stack vent of the lower floors, although functionally there is no problem with doing so, again, assuming the pipe sizes are adequate. A fixture, such as a bathtub, with a high volume drainage discharge could create sufficient velocity during its descent that it could aspirate the water out of the toilet on the lower level, but a lavatory does not have that volume.

  11. #11
    DIY Junior Member CTWeekendWarrior's Avatar
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    Default

    The low heel does go up to the toilet above, but it does not leak now. I suspect the watermarks that are visible are from a prior life. One of the first projects I did after I bought this house was to replace the toilet, although I must admit that I didn't really pay much attention to the plumbing that services the fixture. All of the plumbing pictured was installed before I bought the house, so I can not be sure of the materials, thicknesses, etc. I assume that the plumbing was installed per code (you know what they say about assume!) Perhaps this project is the perfect excuse to revamp the waste lines.

  12. #12
    Master Plumber Redwood's Avatar
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    Default

    The grey pipe is sched. 40 PVC. The grey PVC was common here in the 80's.

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