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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: 29,303, Reputation: 1939
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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: 6,855, Reputation: 479
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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: 52, 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: 5,715, Reputation: 339
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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: 12,591, Reputation: 1180
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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: 52, 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: 6,855, Reputation: 479
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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: 12,591, Reputation: 1180
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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: 29,303, Reputation: 1939
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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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    mygirlsdad77's Avatar
    mygirlsdad77 Posts: 5,715, Reputation: 339
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    #11

    Mar 23, 2009, 03:22 PM

    If you could post a picture of your vent, we could most likely tell you if you need to redo it, or just let it be. Hope to see a clear, staight on pic.
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    luckyrabbit7's Avatar
    luckyrabbit7 Posts: 52, Reputation: 1
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    #12

    Mar 24, 2009, 10:05 AM
    Quote Originally Posted by speedball1 View Post
    Rabbit, 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?
    Tom,
    You shouldn't call any one dense or stupid because they don't get something. I'm just here to learn,not argue about anything. I do see that what massplumber draw was a trap.
    But , that's what he draw to make a point. To have what he drew, I would think you would have to have a wye facing downward at the stack and a 45 connected to the wye to bring the angle back up. If it is connected to the stack with a t, the water, if any, would drain into the stack like a drain connection.

    Quote Originally Posted by mygirlsdad77 View Post
    if you could post a picture of your vent, we could most likely tell you if you need to redo it, or just let it be. Hope to see a clear, staight on pic.
    Mygirlsdad
    I will try to get a picture, but its up in a dropped ceiling. So the straight on shot may be a little off. I was wrong about the way the way the pipes connect . The vent pipe with the wrong angle connects to the vent back of my utility sink. The utility vent pipe
    Goes up to the ceiling, across the ceiling 3 or4 feet, then up. The vent pipe with the wrong angle connects to horizontal run.

    I guess my big concern is what milo said about any gases building up at the high point.
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    speedball1's Avatar
    speedball1 Posts: 29,303, Reputation: 1939
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    #13

    Mar 24, 2009, 11:21 AM
    Tom,
    You shouldn't call any one dense or stupid because they don't get something
    I didn't call you stupid. I just couldn't see why you couldn't grasp the concept of reventing. If you're offended then I apologize.
    I do see that what massplumber draw was a trap.But , that's what he draw to make a point.
    No, he drew it to show you that you were wrong when he couldn't seem to get through with words.
    To have what he drew, I would think you would have to have a wye facing downward at the stack and a 45 connected to the wye to bring the angle back up. If it is connected to the stack with a t, the water, if any, would drain into the stack like a drain connection.
    Wrong again Rabbit To have what he drew you would have to cut a inverted san tee in the stack but have back fall on the horizontal line just the way you describe.
    But how important is the angle of the vent pipe where it connects to the stack? I know it should be a upward slope.
    ( And this is the drawing you showed us) No Rabbit, It slopes down from the stack that's what we've been attempting to tell you. If the vent's trapped b y water in the horizontal pipe then that vent's useless. I wouldn't be too concerned about sewer gas building up in your system.. You have other vents. I would wory more about the backfall closing off your vent which vents the toilet as well as the vanity.. I hope this explains why I was so puzzled by your reluctance to accept our explanation . Regards, Tom
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    luckyrabbit7's Avatar
    luckyrabbit7 Posts: 52, Reputation: 1
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    #14

    Mar 25, 2009, 10:31 AM
    I said that I was confused by the answers from the start.
    In my first question I said the vent should be on a upward slope
    That's when you jump all over me saying your wrong.
    Then I get statements like:
    Quote Originally Posted by Milo Dolezal View Post
    Agree with Tom: yes, vent should have
    Quote Originally Posted by Milo Dolezal View Post
    Agree with Tom: yes, vent should have upward slope of 1/4"per foot.
    of 1/4"per foot.
    Quote Originally Posted by mygirlsdad77 View Post
    drain slopes down to stack, vent slopes up to stack
    When I say it should be upward I'm wrong, when someone else says it , they are right.
    You say the vent and the drain should be exactly the same.
    Quote Originally Posted by speedball1 View Post
    ] The vent will slope back to the stack exactly like a drain..
    Then when massplumber put up his picture:

    I said that you would need wye and a 45 to get what he drew. And you going, your wrong again. See picture below- exactly the same.

    Please show me how you can get that scenario using a tee.
    I welcome everyone's opinion on the whole thing
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    speedball1's Avatar
    speedball1 Posts: 29,303, Reputation: 1939
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    #15

    Mar 25, 2009, 11:50 AM
    Rabbit,
    Is this what you have? (see image)? If so, how hard did you have to work to build your trap? You ask;
    Please show me how you can get that scenario using a tee.
    First off a wye and eighth bend make a combo, That's a combination wye and eighth bend to you,(see image) You have cocked the fitting up at a strain. If the stack's vertical then the 45 should be horizontal and not cocked up. Once more time, is this yours?
    Simple! You just have the other end of the horizontal run at a higher elevation then the branch of the tee( exactly as yiou have shown us.) and , Presto! You have backfall.
    Let's put this thread to bed. If the Picture you've put up is in your basemeny then you've screwed the pooch. Go back and do it correctly. If we can't convince you that you screwed up then I guess you'll just have to live with it. Sorry we couldn't help you but you obviously know more anout plumbing then we do. Tom
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    Milo Dolezal's Avatar
    Milo Dolezal Posts: 6,855, Reputation: 479
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    #16

    Mar 25, 2009, 01:13 PM

    Just rework it: cut that Y and 45, move it 12' higher, reconnect vent below. You are set. I am including my sketch showing what you have and what you should have...

    Btw: who ever did the initial installation was a quack...

    Let us know how you did... Milo
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    luckyrabbit7's Avatar
    luckyrabbit7 Posts: 52, Reputation: 1
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    #17

    Mar 25, 2009, 01:45 PM

    Sorry speedball, I just can't put it to rest, just yet.
    First of all, that's not what I have in my basement.
    I put that together to illustrate what massplumber drew.
    You would have something like that to cause a trap.
    I also said if the connection was just a tee, what would it matter,wouldn't any water just drain back into the stack.
    (That's the point I was called dense)
    Please, once again illustrate what massplumber drew, with just
    A tee. Show me how the water will build up and act as a trap in a tee. Not with a wye with a 45, or 1/8 bend, any kind of combo, just a tee
    And I'll shutup.
    I'm here to learn, not fight or get pissed or piss anyone off.
    I know that everyone here knows more than me.
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    speedball1's Avatar
    speedball1 Posts: 29,303, Reputation: 1939
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    #18

    Mar 25, 2009, 04:33 PM
    One more time Rabbit!
    If the end of the horizontal pipe is higher then the branch of a inverted sanitary tee you have backfall. Enough back fall and you have a trap as the water builds up.
    You have shown us backfall in all your drawings.
    Rule of thumb!
    Slope from the vant stack to the drain= good
    Backfall from the vent stack to the drain= bad
    That's the way things work Rabbit and I can't believe this thread has carried on this far.
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    massplumber2008's Avatar
    massplumber2008 Posts: 12,591, Reputation: 1180
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    #19

    Mar 25, 2009, 06:14 PM
    Hi All:

    Rabbit... you have worked hard to prove your point. I appreciate that.

    I want you to know that all the plumbers here picture so many circumstances that revolve around this issue that you cannot possibly appreciate what we are talking about in some ways.

    The fact is that a sanitary tee fitting can lead to a trap... especially on longer runs where someone has not paid attention to pitch for the vent... so it is possible and it does occur... OK?

    I don't think this is the case for you though...right? If not, then no big deal, but as stated, it happens more than you would think!

    I am sure you are clear on venting now... right? You pop back anytime and let us know if we can help, but this thread should end here... up to you.

    MARK
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