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Thread: Vent question

  1. #1
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    Default Vent question

    Called this out, its a vent in an attic serving a half bath..., it goes up makes a couple turns and 90 down and then later in the line 90 down again then up... anyway, one plumber said it was fine one said it was total crap.. I figured if there were a place to get opinions, this will be it.

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    Default Re: Vent question

    Quote Originally Posted by Marc M View Post
    Called this out, its a vent in an attic serving a half bath..., it goes up makes a couple turns and 90 down and then later in the line 90 down again then up... anyway, one plumber said it was fine one said it was total crap.. I figured if there were a place to get opinions, this will be it.
    If it is sloped so that water can not be trapped I would not worry about it. JMHO

    The beatings will continue until morale has improved. mgt.

  3. #3
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    Default Re: Vent question

    Quote Originally Posted by Vern Heiler View Post
    If it is sloped so that water can not be trapped I would not worry about it. JMHO
    I think that is the issue that I was concerned about. That is, when it does finally make its ascent through the roof deck, that 90 down and back up again later sort-of make a 10' trap. Or am I way off.

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  4. #4
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    Default Re: Vent question

    Quote Originally Posted by Marc M View Post
    Called this out, its a vent in an attic serving a half bath..
    Shouldn't be a problem venting a drain.

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  5. #5
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    Default Re: Vent question

    Quote Originally Posted by Marc M View Post
    I think that is the issue that I was concerned about. That is, when it does finally make its ascent through the roof deck, that 90 down and back up again later sort-of make a 10' trap. Or am I way off.
    If the pipe slopes down in both directions from the elbow in the center of pic #1 it should not be a trap.

    The beatings will continue until morale has improved. mgt.

  6. #6
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    Default Re: Vent question

    I'm having trouble figuring out the direction and elevation changes from your photos.
    Depending on if the arrows indicate air flow or water flow then you may have a problem or maybe not.
    Vent pipes should slope toward the drain just like drain pipes so that condensation and rain water flow to the sewer. If it can trap water, it is a problem. How big of a problem, who knows, but looks like there is plenty of head room to do a fix.

    Jim Luttrall
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  7. #7
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    Default Re: Vent question

    This is a better pic..I drew this. its the entire visible vent in the attic. I do agree there is room to fix.

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  8. #8
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    Default Re: Vent question

    It is crap.

    John Kogel, RHI, BC HI Lic #47455
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    Default Re: Vent question

    Quote Originally Posted by Marc M View Post
    ... one said it was total crap ...
    The plumber who said that is the correct plumber. .

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  10. #10
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    Default Re: Vent question

    Then crap it is...

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  11. #11
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    Default Re: Vent question

    This is why it it crap:
    - From the IRC:
    - - P3104.2 Grade. - - - Vent and branch vent pipes shall be graded, connected and supported to allow moisture and condensate to drain back to the soil or waste pipe by gravity.

    Also, if the vent traps water, then the vent will also trap air, and that defeats the purpose of the vent to an extent as the air needs to be able to free flow into the vent and not have to overcome any pressure in the vent due to "trapped" air.

    Jerry Peck, Construction / Litigation Consultant
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  12. #12
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    Default Re: Vent question

    Quote Originally Posted by Jerry Peck View Post
    This is why it it crap:
    - From the IRC:
    - - P3104.2 Grade. - - - Vent and branch vent pipes shall be graded, connected and supported to allow moisture and condensate to drain back to the soil or waste pipe by gravity.

    Also, if the vent traps water, then the vent will also trap air, and that defeats the purpose of the vent to an extent as the air needs to be able to free flow into the vent and not have to overcome any pressure in the vent due to "trapped" air.
    If it's as Drawn then Wrong.

    Jerry,
    I'll bite. ( no water just air.)
    How do yo trap air in an open pipe?

    - - - Updated - - -

    It Might have Choked Artie But it ain't gone'a choke Stymie! Our Gang " The Pooch " (1932)
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  13. #13
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    Default Re: Vent question

    Quote Originally Posted by Billy Stephens View Post
    Jerry,
    I'll bite. ( no water just air.)
    How do yo trap air in an open pipe?
    Billy,

    That's why put the trapped in quotes.

    Example of a proper vent - vent is vertical or sloped (graded) so that water can gravity drain (which means down) to the base of the vent. Gravity also helps air flow (by not resisting the flow) as the "slug" (in quotes because even though it is not really a slug, that is what it is called) of water from a trap goes down the drain, the "slug" of water creates a low pressure area behind it which helps draw air into the vent.

    Example of the vent Marc showed - two things are likely to happen and which will (can) create a resistance to the flow of air into the vent:
    - Water has accumulated in the trapped section.
    - - If full of water, a lot of driving pressure will be required to move enough water to allow a gulp of air through.
    - - If only partially full of water, the space for air flow is reduced.
    - "Trapped" air. - the driving pressure will need to be greater than for a vent without a trap as the air needs to be "sucked" up before the air can gravity flow down. *I* don't know the pressure difference required to sucked the air up, only that more pressure difference will be required ... and the vent is not intended to require a higher pressure (negative pressure) to properly vent.

    I could be wrong, but I can only see a trapped vent working if a greater pressure is applied.

    I included the trapped water example to show the difference ... the only difference between the trapped water and trapped air is that air weighs less ... but still has weight.

    Jerry Peck, Construction / Litigation Consultant
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  14. #14

    Default Re: Vent question

    Quote Originally Posted by Billy Stephens View Post
    If it's as Drawn then Wrong.

    Jerry,
    I'll bite. ( no water just air.)
    How do yo trap air in an open pipe?

    - - - Updated - - -
    Isn't it obvious. By creating a trap that will hold water you no longer have free communication with the open air when water gets trapped.

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  15. #15
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    Default Re: Vent question

    Quote Originally Posted by JeffGHooper View Post
    Isn't it obvious. By creating a trap that will hold water you no longer have free communication with the open air when water gets trapped.
    Very Impressive Resume Mr Jeff.

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  16. #16

    Default Re: Vent question

    Quote Originally Posted by Marc M View Post
    Very Impressive Resume Mr Jeff.
    Trying to keep up with Jerry!!!!

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