Combining vents. Please proof my layout.

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by whackit, Jun 6, 2014.

  1. whackit

    whackit New Member

    Messages:
    21
    Location:
    Los ANgeles
    Hi All.

    I am designing my vent system and want to have a single roof exit. Here is how it all lays out. I know I have 4" in and 4" out but just wanted to make sure everything else was okay in the middle that was combined. Assume everything else is correct (level over flood rim etc).

    Thanks!

    Attached Files:

    Last edited: Jun 6, 2014
  2. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,247
    Location:
    Cave Creek, Arizona
    The ONLY ones that count are the ones connected DIRECTLY to the 4". That being the case, you have three 2" ones and one 1 1/2". That gives you an area of 3.56 times Pi, while the 4" line is 4 times Pi, so technically, you are a little shy of the requirements, but the inspector might not do the calculations.
  3. whackit

    whackit New Member

    Messages:
    21
    Location:
    Los ANgeles
    Thanks for the reply. I can break out another 1.5 vent pretty easily so that will get me to the right number. I was mostly concerned about the large group on the left that all combines through a single 2" line. I wasn't sure if I would be allowed 2 toilets on a single 2" line. I did the DFU calks and that gives me a total of 18 (i forgot a floor drain on the drawing) and the California code book says I am allowed 24 on a 2" line so I guess that's fine too.
  4. Kiton

    Kiton Member

    Messages:
    61
    Location:
    Quebec
    HJ, how does this get calculated? What is the ideal or required
    Last edited by a moderator: Jun 8, 2014
  5. Terry

    Terry Administrator Staff Member

    Messages:
    15,416
    Location:
    Bothell, Washington
    In California, using UPC plumbing code, you can run three bathrooms on 2"
    However, you do need 4" through the roof if you have 4" going down. A four bath home used 4" when the forth toilet is added.

    You can achieve the 4" area by also using four 2" vents.
    In this case, he just ones a single 4" vent.

    [​IMG]
  6. whackit

    whackit New Member

    Messages:
    21
    Location:
    Los ANgeles
    My high school math tells me: Area = pi x radius2.

    So HJ is comparing the squared radii prior to multiplying by pi.
  7. Kiton

    Kiton Member

    Messages:
    61
    Location:
    Quebec
    I was referring to code requirements and application of, I was told that locally, the only thing that counts was the vent could not be smaller than half the size of the largest pipe it serves in the system. That appears to be an over simplification.



    We generally have a 4 inch servicing the bathrooms and a separate 2 inch servicing the kitchens so I was curious about Whackit's config.
    Thank you,
  8. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,247
    Location:
    Cave Creek, Arizona
    quote; HJ, how does this get calculated? What is the ideal or required

    In most cases, the total AREA of the pipes through the roof should be the same or greater than the area of the incoming sewer line. The simplest way to do the calculation is to take half the diameter of the pipe, square it, do the same to ALL the germane vent lines. Add those numbers together and compare the answer to half the diameter of the main drain squared. Do NOT factor in PI because it is a constant and cancels out.
  9. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,247
    Location:
    Cave Creek, Arizona
    quote; So HJ is comparing the squared radii prior to multiplying by pi.

    You are NOT interested in the actual area, you are making a comparison, and for that calculation, since PI is a constant and cancels out it can be ignored.
  10. Kiton

    Kiton Member

    Messages:
    61
    Location:
    Quebec

    Thank you hj,
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