Size of drain pipe for high performance shower?

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by nofears67, May 23, 2010.

  1. nofears67

    nofears67 New Member

    Messages:
    186
    I posted this thread yesterday and recieved one reply, however now the thread is gone.

    Anyway here it is again...

    I am building a new home my master bath will have multiple (9) shower heads. If running all heads the shower could produce 22.5 gpm. My plumber wants to install a 2" drain pipe and trap but I was thinking it wouldn't be able to handle a "full bore" flow without creating puddling on the floor of the shower.

    Should I have him increase the drain pipe and trap to 3"
    Would having a 3" drain/trap hurt anything under normal flow conditions (5-10 gpm)?

    The main trunk line is already 3".

    Thank you
  2. nhmaster3015

    nhmaster3015 Master Plumber

    Messages:
    836
    Location:
    The granite state
    Sure, have him go with 3" better safe than sorry.
  3. nofears67

    nofears67 New Member

    Messages:
    186
    Is there any concern with having a 3" drain and only feeding it small amounts of water? I ask because my plumber said that sometimes when you oversize a drain it may not function correctly. I can't see how that can be the case unless you have a 6" drain and were only feeding it a couple gallons a minute.

    But even that considered, water just flows through the trap anyway, regardless of the volume (right?). The size dictates the volume capacity under gravity flow, correct?
  4. rmelo99

    rmelo99 Network Engineer

    Messages:
    349
    Location:
    Connecticut
    Depending on the actual size of the shower I have seen some with TWO 2" drains. It will handle all that volume of water and if someone stands on one drain the other one will still empty the shower. Since 2" is more standard, I would think you could be limiting your options for drain styles if you went for a larger size(if you care)
  5. Terry

    Terry Administrator Staff Member

    Messages:
    15,118
    Location:
    Bothell, Washington
    It's only water, how could it plug up?
    You still have a grid that only lets stuff like hair down. and a snake will get the hair if it ever is a problem, which it shouldn't be if the plumber reams the ends of the pipe.
  6. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,129
    Location:
    New England
    At the most, you might have 3/4" supply lines (anything larger is really hard to find). Even if both the hot and cold were running full, most valves won't flow that much. You may need multiple supply lines off of a 1" supply to reach your desired max flow rate without being dissapointed. But, a 2" drain still has a lot more area than the supply lines. If the slope is proper, it shouldn't build up, but there will be a fair amount of depth as that sheet of water moves towards the drain.
  7. Doherty Plumbing

    Doherty Plumbing Journeyman & Gas Fitter

    Messages:
    810
    Location:
    Penticton, BC
    The problem is that unless you are going with a custom shower base/drain you may find it tough to buy a 3" shower drain fitting... I have never seen or heard of one.

    Two 2" shower drains will have just a bit less surface area as one 3" shower drain (if you can find one).
  8. Doherty Plumbing

    Doherty Plumbing Journeyman & Gas Fitter

    Messages:
    810
    Location:
    Penticton, BC
    Last edited by a moderator: May 24, 2010
  9. nhmaster3015

    nhmaster3015 Master Plumber

    Messages:
    836
    Location:
    The granite state
    We do 3" drains fairly often. Looks better and is less hasle to pipe than 2 2" drains
  10. nofears67

    nofears67 New Member

    Messages:
    186
    The supply line size to the mstr shower will be 1.25" copper, ran overhead and then down the wall. There will be two Kohler thermostatic valves installed both capable of flowing 17 gpm each. One will flow 12.5 gpm and the other, 10 gpm, under "full bore".
  11. Redwood

    Redwood Master Plumber

    Messages:
    7,450
    Location:
    Connecticut
  12. nofears67

    nofears67 New Member

    Messages:
    186
    lol...thanks Redwood
  13. Doherty Plumbing

    Doherty Plumbing Journeyman & Gas Fitter

    Messages:
    810
    Location:
    Penticton, BC
    Sounds like you're building a car wash not a shower :D:D:D
  14. asktom

    asktom Member

    Messages:
    575
    Location:
    Victor, MT
    At the risk of offending, I find installing a shower that can crank out that much water to be irresponsible. You live in a desert for cripes sake. Somewhere out there John Wesley Powell is smacking his palm against his forehead.
  15. nofears67

    nofears67 New Member

    Messages:
    186
    Asktom, no offense taken. You have the right to your opinion.

    We have decided to go with a 3" drain in our "car wash". :p

    Thanks everyone!
  16. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    There was a server upgrade over the weekend, but some posts were lost in the process.


    ►yes, use a 3" drain. The DFU and gpm specs from the UPC would mandate that, as I see it.
    ►please contact algore immediately....he is just DYING to hear about this monster!
  17. nukeman

    nukeman Nuclear Engineer

    Messages:
    711
    Location:
    VA
  18. nofears67

    nofears67 New Member

    Messages:
    186
    The rough plumbing has been completed but I noticed that my plumber has not installed the traps that would be underneath the showers...There are supposed to be traps installed correct? Are these done right before the slab is poured or what?

    I'm asking here because I haven't talked to him yet.

    Thanks
  19. Terry

    Terry Administrator Staff Member

    Messages:
    15,118
    Location:
    Bothell, Washington
    It would be a waste of time to set the traps before the concrete pour.
    Have you ever watched a concrete poor? They are like a bull in a china shop.
    You want them exact right?
  20. nofears67

    nofears67 New Member

    Messages:
    186
    So does that mean the slab won't be poured in the areas where the shower drains will be located?

    Of course I want them exact. ;)
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