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    Angle of vent

    Asked Mar 22, 2009, 09:17 AM 18 Answers
    I know that a drain pipe is sloped downward 1/4" per foot to where it connects with the stack.
    But how important is the angle of the vent pipe where it connects to the stack?
    I know it should be a upward slope.
    I noticed that I have a vent pipe that connects downward more like a drain.
    Should I go through the effort of changing this?
    Thanks jim

    Last edited by speedball1; Mar 22, 2009 at 09:35 AM.
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    18 Answers
    speedball1's Avatar
    speedball1 Posts: 28,574, Reputation: 1906
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    #2

    Mar 22, 2009, 09:42 AM


    I know it should be a upward slope.
    ] If you're referring to the fall from the vent to the stack you are incorrect
    I noticed that I have a vent pipe that connects downward more like a drain.
    Should I go through the effort of changing this?
    Yes! You should go back and do it correctly. The vent will slope back to the stack exactly like a drain.. That's because it will drain away any rainwater that collects in the pipe brfore it builds up into a trap and bloc ks the vent from venting. Good luck, Tom
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    Milo Dolezal's Avatar
    Milo Dolezal Posts: 6,039, Reputation: 393
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    #3

    Mar 22, 2009, 09:47 AM



    Agree with Tom: yes, vent should have upward slope of 1/4"per foot.
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    luckyrabbit7's Avatar
    luckyrabbit7 Posts: 50, Reputation: 1
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    #4

    Mar 22, 2009, 04:53 PM

    I more confused by the answers I received.speedball1 says: That I'm incorrect when I say that the vent should
    Have an upward slope. He then says:The vent will slope back to the stack exactly like a drain

    Milo says he agrees with tom and it should have an upward slope.
    The two answer seem to be opposite.
    Help
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    mygirlsdad77's Avatar
    mygirlsdad77 Posts: 5,705, Reputation: 336
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    #5

    Mar 22, 2009, 05:03 PM



    Drain slopes down to stack, vent slopes up to stack. Both should be 1/4 inch per foot. Although, my book says vents can be level(but if possible sloped upward to stack. ) Im not that good with drawings, but I'm sure one of these pros will give you a pic of what they are talking about.
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    massplumber2008's Avatar
    massplumber2008 Posts: 11,866, Reputation: 1113
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    #6

    Mar 22, 2009, 05:19 PM
    Hi Rabbit...

    A vent always pitches back toward the drain so rain water that gets in through the roof vent can travel to the drain pipes BY GRAVITY.

    A waste line always pitches upward so waste drains by gravity (I know you know....we have worked together before!).

    See my picture below.

    If your vent pitches in such a way that it cuts off more than 1/4 of the vent pipe from draining back toward the drain then I say you change it. If not... leave it be...

    My opinion...

    MARK
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    luckyrabbit7's Avatar
    luckyrabbit7 Posts: 50, Reputation: 1
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    #7

    Mar 22, 2009, 11:50 PM
    Massplumber2008
    I agree with everything you said. I know the way it should be, but I guess my real question is that I don't see what difference its makes. If the vent pipe is connecting at a downward angle, the water coming down would never enter it or it would drain back out. I changed your picture to reflect the way mine looks.
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    Milo Dolezal's Avatar
    Milo Dolezal Posts: 6,039, Reputation: 393
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    #8

    Mar 22, 2009, 11:56 PM

    LuckyRabbit: That vent is a gravity vent . It sucks air IN as sewage flows down the drain ( Law of Physics: displacement) allowing it to flow without inhibition.

    But also, it vents your main sewer line. Warm, moist, sewer gases raise through the vent system to the roof. If the vent system is NOT sloped upward - as shown in your latest post, than sewer gases won't raise, will accumulate, will condensate, will flood the backward pitched section of vent - and eventually blocking it and preventing air from flowing through. Drainage problem will occur...

    That's why the upward pitch of vents is as important as down slope of drains...
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    massplumber2008's Avatar
    massplumber2008 Posts: 11,866, Reputation: 1113
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    #9

    Mar 23, 2009, 05:00 AM
    Hi Lucky...

    Milo presented good information and I just wanted to add a little more...

    Rain water will flow down the stack and it will enter the fitting for the vent... whether a wye fitting or a sanitary tee fitting... and as you can see, over time can fill with rain water and condensation and can acummulate and effectively cut the vent contribution to drainage down to almost nothing... depending on the angle of the vent. See picture.

    Never mind the fact that most vents don't just connect into a stack like in this case. A lot of the time vents can run for 20, 40 or 60 feet or more with all kinds of twists and turns. If any of these pipes get back pitched or say a couple sections of a long run get back pitched you can see where problems can start to pop up...

    Anyway, that is my thoughts on this... like I said, if your pipe is pitched back so it could fill and reduce effectiveness of the vent then I would fix it. If minimally back pitched then leave it alone...

    Have a good day!
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    speedball1's Avatar
    speedball1 Posts: 28,574, Reputation: 1906
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    #10

    Mar 23, 2009, 05:47 AM
    And what Massplumber put upis called a trap. And a trap defeats the vent process..
    I believe I brought that up in a earlier post,
    The vent will slope back to the stack exactly like a drain.. That's because it will drain away any rainwater that collects in the pipe brfore it builds up into a trap and blocks the vent.
    Rabbit,
    I guess my real question is that I don't see what difference its makes.
    Why are you being so dense about this? Can't you see, (Massplumber does in his image) that you have built yourself a trap in your drawing?
    Take our word for it. Slope is very important in a vent! Period! Regards, Tom
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