Flat Vent

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Tom Sawyer, Jul 6, 2011.

  1. Tom Sawyer

    Tom Sawyer In the Trades

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    I would like to clear up some confusion here regarding the practice of flat venting. I fully realize that in some states it is perfectly legal and acceptable to inspectors. I want to show you why it should not be though, and that just because a thing can be done it is not always the best reason to do it that way. Take a look at the picture here. This is an acceptable ( to some ) method of venting a water closet. The wye fitting which is being used for the vent has been rolled up so that its run inlet is above the center line of the horizontal drain. So far so good. Where this goes wrong is the horizontal pipe that heads back to the wall parallel to the WC closet bend and then it runs up the wall and presumably to another vent or through the roof. At any rate, that horizontal piece of pipe can and will eventually fill with toilet paper, tampons, condoms and poo and it will plug up thereby negating it's intended use. Better that the vent continue to rise vertically until it has reached a point (6" above the highest fixture served which is the lav) and then it can go horizontal because it won't be subjected to all the nasty stuff that can clog it up.

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    Last edited: Jul 7, 2011
  2. hj

    hj Moderator & Master Plumber Staff Member

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    "Stuff" will only get into that flat vent when the toilet drain line plugs up, but once it gets into that pipe, unless there is some way to dislodge it, it will stay there. That is why flat vents almost ALWAYS are required to have some other fixture, such as a sink, connected to it to keep it flushed out. A cleanout would be a less than desirable alternative because you would NOT use it unless you KNEW the vent was plugged.
  3. Tom Sawyer

    Tom Sawyer In the Trades

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    Yes but a fixture attached makes it a wet vent and in it's current configuration you would never know if it was plugged or not because the toilet is going to flush just fine anyway because it does not need a vent to operate.
  4. hj

    hj Moderator & Master Plumber Staff Member

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    You are addressing a flat vent, and the normal configuration for a flat vent IS a wet vent to eliminate the problem you have discussed.
  5. Tom Sawyer

    Tom Sawyer In the Trades

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    HJ, you are probably from an area where you just don't run into a true flat vent. Massachusetts allows them and up until a couple years ago Maine did also. I think it is confusing though to call a flat vent a wet vent. Lord know enough plumbers get confused over what constitutes a proper wet vent.
  6. plumber2011

    plumber2011 Expert Plumber

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    As HJ said, "That is why flat vents almost ALWAYS are required to have some other fixture, such as a sink, connected to it to keep it flushed out". I see no issue with flat venting as long as the horizontal run is as short as possible AND a sink and/or tub are connected...see image.

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  7. Yersmay

    Yersmay Writing, constructionDIY Member

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    A question

    Tom, I'm curious about something you said in a few posts up in this thread. You said that a toilet does not need a vent to operate. I guess this makes sense because a toilet evacuates via a siphon, so I suppose a toilet is a big brother to an 'S' trap. Would a toilet have an even more powerful flush without a vent? If a toilet has a built in weir which keeps the sewer gasses out of the house, why then is a vent required on toilets? Does the vent have less to do with the toilet itself and more to do with keeping things moving in the waste line downstream of the toilet? Thanks in advance! Interesting thread!
  8. Gsalet

    Gsalet George the Plumber

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    have you ever put your finger over the end of a straw that was in a soda then removed the straw from the soda? notice how the soda stays in the straw, now release your finger and see how the soda drains from the straw. without a vent the toilet might flush but would not drain.
  9. Tom Sawyer

    Tom Sawyer In the Trades

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    The diagram you have there is not a flat vent it is a wet vent. You guys need to understand your definitions a little better to avoid confusion. A true flat vent is not washed at all which is why it is not allowed in most places. I see no issue with wet venting, it is pretty much standard procedure.
    Last edited: Jul 7, 2011
  10. Tom Sawyer

    Tom Sawyer In the Trades

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    There is so much misunderstanding about what vents are for, even by experienced plumbers. Vents protect the trap seal. Without traps, there is no need for a vent at all. Toilets are self siphoning and incorporate a full S trap in their design. A toilet will flush just fine with no other vent than the atmosphere pushing down on it's open bowl. To prove this point I attached a working toilet to close to 60' of 3" pvc with no vent at all and the pipe pitched at 1/8" IPF. The toilet flushed perfectly every time. we filled it with wet paper towels, it still flushed perfectly every time and the reason is because the toilets bowl is the vent. Then again ANY fixture will drain just fine with no vent for the same reason. If a plugged vent is causing the fixture to drain slowly it is because the drain itself is plugged not the vent.
  11. Tom Sawyer

    Tom Sawyer In the Trades

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    That is just plain not true at all.
  12. plumber2011

    plumber2011 Expert Plumber

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    Yet here at this thread (click below) where I drew up a WET VENT (post #9) you called it a FLAT VENT (post #10), Tom?? In fact, that is what started this thread...isn't it? Yet all I was proposing in that thread was to roll the wye up as shown above and use the tub to wet vent the toilet...again, you called it a flat vent???

    http://www.terrylove.com/forums/sho...throom-DWV-in-floor-on-slab-...-no-wall-space

    I think it's you that need to get things straight...;)

    PS: I also disagree completely with your assessment of venting as presented here, Tom! *SHRUGS*....dunno, just dunno!
    Last edited: Jul 7, 2011
  13. Tom Sawyer

    Tom Sawyer In the Trades

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    Take another look at your post #9. The section from the vertical vent to the tub wye in particular. That flat section of pipe there is not washed by any fixture above as drawn and is therefore a "flat vent"

    That you disagree with my assessment of venting comes as no suprise to me. You disagree because you really do not understand venting. To qualify my statements though. I have been a master for 37 years now. I teach plumbing apprentice classes as well as licence recertification seminars. I was a state plumbing inspector for a few years and local plumbing inspector as well. I currently teach plumbing at a high school technology center and hold a masters in plumbing design and education.
  14. plumber2011

    plumber2011 Expert Plumber

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    Again, you are mixing terms here. That is a wet vent....period!

    I'm not going to go into exactly how many engineering degrees, or prosthetics and electrical degrees I have...not important to prove anything to you. You also can't insult me or even upset me as your opinion is not importanmt to me, Tom. Suffice it to say, again, that I disagree with you...completely!
  15. Tom Sawyer

    Tom Sawyer In the Trades

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    NO it is not a wet vent. The flat section that rises to vent is NOT washed by any fixture avove therefore it is NOT a wet vent.

    Nobody is trying to insult you here at all. Enlighten perhaps but not insult. You can disagree all you want, that's your right but before you do I suggest a little trip through your code book will change your mind.

    The title of this thread is "Flat Vent" not wet vent. There is a difference and that difference is shy I started this thread.
    Last edited: Jul 7, 2011
  16. plumber2011

    plumber2011 Expert Plumber

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    The flat section that rises to the vent won't have any solids introduced to it as the wet vented section is washed by the tub. You are picking at very subtle issues here, Tom and it is NOT helping anyone at all.

    Have a good day. I'm off to work but will check back later tonight!!

    Thanks!
  17. hj

    hj Moderator & Master Plumber Staff Member

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    quote; HJ, you are probably from an area where you just don't run into a true flat vent.

    Several years ago I was installing the plumbing for bakery departments in grocery stores. All of the installations were basically similar. About the fourth one, when I took the isometric to the building department, they said I could NOT install the system that way, regardless of how it had been done previously. When I asked, "How can I install it then?", they said to take it over to "Joe" at the adjacent desk. Joe then proceeded to revise my drawing. When he finished he had "true" flat vents on all the floor drain lines. When I protested, "You cannot do that", he said, "Yes you can under the new code". Since the revisions were simple to incorporate into the piping we had already installed, I told him, "okay, send the inspector out this afternoon". When the inspector arrived he took one look at the installation and rejected it because of flat vents, but then I showed him the approved drawing. He looked at it, then at the installation, and asked, "Where is the telephone?" He called his senior inspector and told him, "These guys have an installation with flat vents and a drawing approved this morning showing them. What should I do?" The boss told him, "Have the person who approved the drawing, make the inspection and approve it." I told the inspector that as soon as he left, concrete was going into the trenches, regardless of whether he approved it or not. He did, but 30 minutes later he came back and said, "As of this minute, we are back on the old code". Six months later on another job, he said, "Aren't you the same guys who did the grocery store bakery? Can you redraw the isometric for the installation, because ALL of the paperwork for that job has disappeared." NO self respecting code authority should EVER approve a line which could become obstructed and not be able to be cleared, OR give sufficient indication that it is not working. IF the drains can function with a plugged vent, then the vent was NOT needed in the first place.
  18. Tom Sawyer

    Tom Sawyer In the Trades

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    The tub inlet to the wye is downstream of the horizontal section which means it will not be washed by the tub. Those subtle issues are what causes plumbing inspectors to fail the job. When I was inspecting these sort of "little" issues came up every day and every day some plumber would get pissed off when the job failed. Close enough is NEVER good enough. Pointing these issues out is very helpful and what these forums are all about.

    thank you for that story HJ and your dead on commentary. Over the years I have run into more licensed plumbers that really have no clue what venting is about than I care to remember. It's amazing how something so simple can be so confusing.
    Last edited: Jul 7, 2011
  19. hj

    hj Moderator & Master Plumber Staff Member

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    quote; [Then again ANY fixture will drain just fine with no vent for the same reason. If a plugged vent is causing the fixture to drain slowly it is because the drain itself is plugged not the vent.

    A "plugged vent" by itself will NOT cause a fixture to drain slowly, in fact it may cause it to drain even faster. The only time it can prevent drainage is if the downstream line is also plugged so the "slug of air" between the stoppage and the trap cannot escape through the clogged vent.
  20. Tom Sawyer

    Tom Sawyer In the Trades

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    HJ, you are absolutly dead on right there. Every plumber should read and fully understand that post. I set up a lab demonstration of that very effect for a 20 dollar bet on another forum awhile back. Still have not got the 20 bucks yet LOL
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