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Thread: size of shower drain pipe

  1. #1

    Default size of shower drain pipe

    We are putting in a new master bedroom and bath and I have a question about shower drain size. Our shower will be 3' 4" by 5' 9" and it will have 3 shower heads hooked up to a 3/4" thermostatic valve: one regular head, one handheld on a bar on the opposite wall, and a rain-type head on the long wall. The two regular heads are rated at 2.5 GPM but can go up to 5 GPM with the flow restrictor removed. The rain-type head will do 6 GPM at 45 PSI. The only time more than one shower would be going at any one time would be if one of us uses the regular shower head and the other uses the handheld. Is a 2" diameter drain pipe adequate? Our plumber has just roughed in a 2" drain but I am concerned since a few people have mentioned that in their spa-type showers they don't get adequate drainage (I don't know the details of their setup, but I would imagine they wouldn't be less than 2" since they are new).

  2. #2
    DIY Senior Member plumguy's Avatar
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    As long as it is properly vented 2" is suffice for a shower.

  3. #3

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    Thanks. So that means a 2" pipe is capable of draining at a rate of 10 GPM--is there any way to look that sort of thing up?

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Well, think of it this way - what size pipe are you using to supply the shower? the area of the drain is quite a bit bigger than that supply (pi r^2 say 3/4" supply = 0.44sq in vs 3.14sq in)...yes, there is a pressure difference, but gravity does work to speed it along.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  5. #5

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    Jim,
    Although the size of the shower pipe might have a small effect on the pressure drop, it doesn't have a big effect on the volume of water delivered, and it's that flow that counts. I just want to know if I'll be standing in a lot of water if I run 6-10 gallons/min.
    Rob

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    DIY Senior Member sulconst2's Avatar
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    Quote Originally Posted by RBKM
    Jim,
    Although the size of the shower pipe might have a small effect on the pressure drop, it doesn't have a big effect on the volume of water delivered, and it's that flow that counts. I just want to know if I'll be standing in a lot of water if I run 6-10 gallons/min.
    Rob

    whats your options? 3"? i checked charlotte pipe and a 3" solvent weld p-trap is approx. 12" tall. unless you are in a slab it would be tough to fit.

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    Plumber jimbo's Avatar
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    What size WH do you have given that a modest 10 minute shower will need 100 gallons?, mostly hot.

  8. #8

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    Jimbo,
    We currently have a 40 gallon WH but our plumber is suggesting that we go to a 75--that was actually going to be a question I left to another thread. I don't think we'd actually use 10 GPM from the HW--probably more like 70% fo that, given mixing, but you're right--a ten minute shower would easily exceed that capacity. But I don't think we would ever really have both showers going simultaneously for ten minutes--the typical scenario for us to have both going would be if we're in a rush to get somewhere and we need to get ready quickly and both shower. It's those times that made me wonder about the 2" capacity.

    I think we will be fine with the 2" drain, and putting in a 3" would require more work than it's worth, as has been suggested. So the next question is, should we upgrade the HW heater. We are currently in a 2300 sq ft house, with 3 full bathrooms (once this new is finished) and 4 bedrooms. There is one bathtub--I think it's larger than usual (it has jets) though we don't use it often. Right now it's just the two of us, but we're having a baby in a few months and would like to have another in a few years. So that does mean the bathtub will get more use. But a 75 gallon HW heater seems like overkill for a small family without teenagers. Any thoughts?
    Rob

  9. #9
    Retired Defense Industry Engineer jadnashua's Avatar
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    A 2" drain is over 7x the interior volume that a 3/4" pipe has...unless it is clogged, you should never be standing in water. Most showers are plummed with 1/2" pipes, so the drain is 16x larger than the supply.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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