combination waste and vent question

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by perrycat, Aug 29, 2007.

  1. perrycat

    perrycat New Member

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    I'm "studying" for taking the journeyman's test, and this book with these practice questions has some about definitions....here's the question:

    A plumbing system that is designed with the waste piping embodying the horizontal wet venting of one or more sinks or floor drains by means of a common waste and vent pipe that is adequately sized to provide free movement of air above the flow line of the drain is known as:

    a. a combination waste and vent system
    b. an engineered system
    c. an illegal system

    .....now, I figure the answer is "A", but really, reading this, I can't see the difference of what they're talking about and just what I understand to be called a "wet loop" like in high rise construction apartment buildings.
    Can anybody give me a short version example or know of an online diagram of a combination waste and vent system that I can look at to try to understand what it is?
  2. FloridaOrange

    FloridaOrange Plumbing Designer

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    Sorry, not in the mood to bust out cad but...

    Picture a 4" sanitary line. You pick up floor sinks/drains on either side say 4 for example. You might also have a couple of sinks on the line. Anywhere on the 4" line you have a 3" vent (inline) that is not picking up anything. If an illustration doesn't show up while I'm having dinner I'll post a cad drawing.
  3. FloridaOrange

    FloridaOrange Plumbing Designer

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    Also, look for an "illustrated" code book. They usually have lots of good stuff in it.
  4. perrycat

    perrycat New Member

    Messages:
    39
    thanks

    I'm going to order one tonight, I was checking out books and I found this one called The National Plumbing Code Handbook by R. Dodge Woodson....now our area now uses the IPC so maybe he's got one for IPC but NPC is better than nothing for examples.
    Last edited by a moderator: Jun 9, 2014
  5. FloridaOrange

    FloridaOrange Plumbing Designer

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    Make sure it's illustrated. IPC vc. NPC isn't really too big a deal. The main concepts remain.

    Here is a combination waste vent on a project that I'm working on. The 3" vent through roof could be anywhere on the system. The 4" carries to the las floor drain in line, the 3" that continues is a branch. That branch could be 2" but due to elevation issues we carry it as a 3" to the sink. On this system we could add alot more floorsinks and such as long as they are attached to the main line. The one floorsink with a vent was because it was about 14'. We can go 10' on a 3" or 12' on a 4" but beyond we would need to vent. Any other questions I could answer I would be happy.

    Just to give you my background, I am a designer for an engineer. The info given by the real plumbers here is invaluable, pump them for whatever info you can. That's one reason I come here, so I can get exposure to situations, fixes and real world issues. Good luck with your education, being a plumber, you'll never want for work.

    Attached Files:

  6. perrycat

    perrycat New Member

    Messages:
    39
    Thanks much

    okay, now I get it, thanks much. I think the "wording" was messing me up....it's just groundworks (horizontal piping I guess), which is including both the waste and vent. I thought it was a special case thing or something.

    But...another question: You said the 3" vtr can be anywhere on the line in the 4" and this is something that's been confusing me for a long time.....shows how much I don't understand venting too.....


    But in your drawing, the 3" vtr is before the mop sink, correct? I thought a vent has to be after all the fixtures. Like say if you were roughing in a simple basement bathroom, everything draining into the 4" AFTER the closet bend..., the vent doesn't have to be the last thing on the line? So I guess my question is when is it that the vent has to be after everything? Or doesn't it matter?

    And I know I ought to know this stuff, and that's why I'm asking, I'm out doing this stuff, and the apprenticeship classes are starting this coming week, and I quit after the second year due to missing classes because we worked late all the time....but I'm thinking of getting back in the apprenticeship and not just taking the test......even if I could pass it, which I doubt right now. So I can get a better understanding of how vents work, hell, how grease interceptors should be plumbed....I can follow someone else's directions and do something the way they tell me to, but that's not a mechanic, thats......a helper.
  7. FloridaOrange

    FloridaOrange Plumbing Designer

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    1,317
    Location:
    SW Florida
    The 4" line acts as a vent. For other system types the fixtures I showed could be on a 3" line, such as a circuit vent. The oversized horizontal drain acts as a vent. So the placement of the 3" vent really becomes immaterial as long as it attaches directly to the 4" line. The line should never be even half full during heavy use so there's always available "air" to vent the fixtures. **I have seen combination waste vents where sinks aren't vented, I do not agree with this but somebody certified it then an inspector OK'd it.

    See my answer above. A simple basement bathroom cannot be vented with a combination waste, no toilets on this system. A vent has to after all fixtures only if a system needs a relief vent. More than 3 toilets on a circuit vent requires a downstream relief vent. Sometimes a downstream vent can be added to help things flow better but not be required. If you were to tie together multiple stacks from above and you have a bathroom on that floor you might want to add a relief vent even though it wouldn't be required.

    Your doing it the right way. No one was born knowing plumbing inside and out, except maybe Grumpy but I'll reserve that opinion for now :). Keep an open mind and always be willing to learn and you'll do alright. If you have any questions I'll try to answer the best I can (I don't know it all either).
  8. FloridaOrange

    FloridaOrange Plumbing Designer

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    Location:
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    Another point about wording....sometimes you need to read between the lines. Code is a form of law, the intent is sometimes more important than the actual words.

    Currently in my code you must tie in downstream of a bathroom wetvent with non-bathroom fixtures. If you have a lavatory on a wall and the owner wants to put a sink on the other side, the new sink would have to be tied in downstream, when the new sink would work all day long tied to the same stack as the lavatory. I have to do it but on some projects I've actually told owners to avoid the extra cost of trenching downstream and have a plumber come in 1 or 2 months after their final inspection and tie into the lavatory.
  9. hj

    hj Moderator & Master Plumber Staff Member

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    Location:
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    cw&v

    The first requirement is that the horizontal line has to be adequately oversized so it can never be completely full of water during normal usage, because the upper portion is carrying the air to create a vent. There has to be a vent at the upper end of the line to allow air in, and one at the lower terminus to relieve any postitive pressure caused by the water flow. The floor drains have to be reduced to a smaller size, usually 2", to limit the gpm flow into the horizontal pipe. The CW&V lines have to be installed to the minimum grade to minimize velocities and prevent creating "S" traps.
  10. FloridaOrange

    FloridaOrange Plumbing Designer

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    Location:
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    I agree with the first two statements but disagree with the rest. I'm not trying to pick a fight, just like good debate because maybe I'm missing something.

    There is no requirement for an upstream vent. The previously mentioned oversized horizontal provides the vent.
    The vent can be anywhere on the horizontal as there is no real positive pressure. Floor sinks never take a full load like a toilet would create and the oversizing slows the waste down which would not create positive pressure.

    Floor drains do not have to be 2", 3" is fine, again related to my comment above about floor sinks.
    minimum grade is 1/8" per foot for a 4" line. I agree that you cannot go to a greater slope however.

    How would minimizing the main slope eliminate "S" trapping as long as you don't create an "S" trap?
  11. The answer is

    C in my state!!!!

    No exceptions either. Period
  12. FloridaOrange

    FloridaOrange Plumbing Designer

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    Location:
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    I see that. Thankfully my state allows wet vents, common vents, circuit vents, combination vents and gut vents. I think venting every single fixture, while works of course, is unnecessary and puts an extra burden financially on the owner of the building. The other systems work just as well when installed correctly.

    What would you do in a situation of a restaurant with no interior walls in the kitchen and all traps greater than 12' from a wall?

    At least what I saw in the KY codebook is 100 times better than what I saw plumbed in GA. Circle traps, unvented....and worse.
  13. The director of the division of plumbing in my state (KY) sees it quite differently as I agree with the sentiment that plumbing systems should be designed to follow maximum load factors, not minimum. Plumbing is designed to work error free and when you run waste through a line dedicated for venting, it compromises the risk for vent failure strictly by the changing of the inner dimension by buildup/debi....reactive qualities such as cast iron/copper/galvanized that has a proven history of clogging due to acidic waste from food and detergents that slowly distort it's once smooth inner surface. KY and NY run the roost in the United States for having the strictest plumbing codes to govern by. I'd rather not know any other laxed code.

    Anyone that's been in plumbing long enough and seen enough piping situations can also verify that even SCH40 PVC can get inner wall buildup from lack of proper venting....even on a vertical drop. All piping can suffer from this situation because the system is not running error-free either by design (wet venting for sure) or lack of proper maintenance.

    I'd follow KY state code provisions and island/loop vent every one of those fixtures with a minimum 2" drain and 3 cleanouts serving different access points to allow proper cleaning. Anything else IMO is a secondary system that leads to reliability of preventive maintenance to keep it running efficiently. In the theory "Every drain must have a vent" in KY....this allows the system to run in simple fashion without preventive maintenance at all...unless the system is abused or overloaded for whatever reason by the end user.

    The statement out financial burden? That's a non-theory in the book of many as the property owner has to have an understanding of what was lost to begin with, what system offers a better design. This isn't of personal choice most times as it is dictated by the local authority in the state they reside in.



    When I took my journeyman's in Ohio with my eyes shut, the head honcho Elmer Weil told me I didn't have to do all that venting on the isometric drawing as it was overkill in Ohio. He said it will work but I won't be deducted points for doing so.

    I aced that journeyman's test and left the connect-the-dot plumbing to someone else. What's really good is new construction in OH is following KY code closely on their new residential home construction. It was not that way years prior.

    I have "issues" with product choices the state of KY allows to be used, along with certain other specifications that should be changed/modified to stop the constant repeat problems they create down the road....affecting the property owner financially. I was able to get enforcement of strapping of expansion tanks in the northern kentucky area.....I'm still working on getting all kitchen sink drains on horizontal runs supported at 2' intervals instead of the norm, 4'. This will solve a true plumbing defect that homes experience within a short few months of use and this is not following the true guildelines of plumbing principles set forth in all of our plumbing codebooks.
    Last edited: Sep 1, 2007
  14. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,874
    Location:
    Cave Creek, Arizona
    code

    You can take exception to it if you want, but every jursidiction I have been in since apprentice school REQUIRED a downstream vent at the end of the CW&V system, and an upstream one to admit air to the upper, vent, portion of the system. The Cabrini Street testing laboratory can show you why they are needed.
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