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Thread: GPM Capacity of 2" Shower Drain

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    Default GPM Capacity of 2" Shower Drain

    Greetings gang and thanks in advance for any help:

    we are remodelling our shower and are looking to put in multiple shower heads and some body sprays.

    our current drain is 2".

    My question is what is the maximum GPM flow that this drain will handle? Also, is there somewhere on line where I can look at the calculations, etc?

    Thanks again for any help.

  2. #2
    Homeowner Thatguy's Avatar
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    Quote Originally Posted by GAtkins View Post
    Greetings gang and thanks in advance for any help:

    we are remodelling our shower and are looking to put in multiple shower heads and some body sprays.

    our current drain is 2".

    My question is what is the maximum GPM flow that this drain will handle? Also, is there somewhere on line where I can look at the calculations, etc?

    Thanks again for any help.
    http://www.engineeringtoolbox.com/pr...pes-d_404.html

    http://www.engineeringtoolbox.com/da...ion-d_646.html

    You need to know pipe length and height above the opening into the next larger pipe, pipe materials, # of elbows, etc.
    Last edited by Thatguy; 08-03-2009 at 02:40 PM.

  3. #3
    Retired Defense Industry Engineer jadnashua's Avatar
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    Assuming you don't have anything greater than say 1" pipes supplying water, it should not be a problem. Now, if it is a really large area of shower, you may want a second drain to limit how far the water has to go to get to the drain.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  4. #4
    DIY Senior Member TedL's Avatar
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    I'm not sure that the links above are an answer, as they deal with pressurized flow, and you're asking about gravity flow.

    I think you can get a workable answer, though not exactly to the question you asked, by looking at your code to see how many fixture units it assigns to the shower heads and how many it allows for the drain pipe size. You're going to have to work within that code if you plan to pass inspection.

    Here's the IPC as an example, not intending to say it controls for you.

    http://publicecodes.citation.com/st/index.htm

  5. #5

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    Thanks for the help so far, but I remain confused.

    Arkansas has adopted the codes in the link. Our house was built circa 2003.

    our master bath shower has a 2 inch drain, 1 shower, 1 toliet, 2 sinks, 1 bath tub separate from the shower.

    the remainder of our house has 2 additional toliets, 3 additional bath sinks, 1 kitchen sink, and 1 washer.

    If I total this up correct with what I have, it comes to 22 units. The rating for a two inch drain if I am reading the table correctly calls for a maximum unit value of 21 for a 2 inch drain with only one quarter inch of slope per foot.

    for a slope of one half inch per foot, it apparently allows up to 26 units.

    I want to add to my existing master show 1 additional shower head (total of 2), and 4 body sprays. The gpm rating of the two shower heads will be 2.5 gpm each for a total of 5 and for each of the body sprays 1.75 gpm for a total of 7 for the sprays and a grand total of 12 gpm for the entire shower.

    When I consulted my plumber this afternoon he said that the maximum GPM for a 2" drain is 12gpm, so according to him this will work.

    I would like to get some independent confirmation of this.

    Will the above work with a 2" drain?

    Thanks again in advance for any help/replies.

    I don't want to remodel the entire shower and then not have it drain.

    Glenn

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    Homeowner Thatguy's Avatar
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    Quote Originally Posted by GAtkins View Post
    The rating for a two inch drain if I am reading the table correctly calls for a maximum unit value of 21 for a 2 inch drain with only one quarter inch of slope per foot.
    That's what I get from my 2000 IRC, assuming no water closets: 21.

  7. #7
    Retired Defense Industry Engineer jadnashua's Avatar
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    I think you're missing something...your toilet drain is at least a 3" pipe, and the whole house may go into a 4" pipe. The outlet of the house drain system is at least 3".
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  8. #8
    ACO Shower Drain Sales johnfrwhipple's Avatar
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    Default Flow Rates of a 2" Shower Drain

    I found this old post and thought I could add in my own two bits.

    I have done a load of private testing on the subject of flow testing and have found many of these 2" drains can handle easily between 8-16 GPM (Gallons Per Minute). In my tests most drains see no build up of water (above grate) at 8-10 GPM or less. When the flow rates creep up higher so does the water level above the grate.

    At 18 GPM I have measure 3/8" of water above the drains grate.

    We have also noticed that flow rates drop when the drop to the P-Trp is not vertical. We also noticed that the higher the drop the better the flow rate. We have also noticed that any mis installed fitting can greatly lower the flow rates.

    Hope this helps.

    Quote Originally Posted by GAtkins View Post
    Greetings gang and thanks in advance for any help:

    we are remodelling our shower and are looking to put in multiple shower heads and some body sprays.

    our current drain is 2".

    My question is what is the maximum GPM flow that this drain will handle? Also, is there somewhere on line where I can look at the calculations, etc?

    Thanks again for any help.


    jfrwhipple@gmail.com - www-no-curb.com - 604 506 6792

    Always get construction advice double checked by your local city hall. Flood Test Every Shower - Every Time.

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