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Thread: 1/2" to 3/4" copper to shower spa

  1. #1

    Default 1/2" to 3/4" copper to shower spa

    Hello,

    Am remodeling bathroom and adding a shower spa with jets that ideally uses 3/4" supply. My problem is that there is only 1/2" copper going to bathroom now. Is it feasable to tee into existing 1/2" and go out to shower with 3/4" copper pipe?

    Thanks....

  2. #2

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    1/2" supply is no problem for filling a tub or running your normal shower. If the jet(s) have a pump that circulates water then once the tub is filled it is a moot point.

  3. #3

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    Actually the new bathroom will have a shower with multiple jets that spray while you are showering.

  4. #4
    Homeowner geniescience's Avatar
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    Default yes. Also, yes and no too.

    yes d.r. you can put a 3/4" pipe after a 1/2" pipe, and it will help a bit by reducing the friction that slows down the flow of water.

    However your 1/2" pipe does have a true physical mechanical maximum flow rate which will prevent multiple jets from getting the optimum or the maximum flow. So no, it is not really advisable by any objective standard to leave a 1/2" in the wall as your supply pipe, not even for a short run. The longer the run, the more the friction which slows down the flow even more.

    Somewhere in the basement, where your water supply comes into the house, the pipe is larger than 1/2". Where your pipe gets reduced down to 1/2", is where the greatest "bottleneck" begins and higher friction prevents water from flowing as fast as it will need to if you want multiple multiple jets to work as they might...

    When a long length of pipe is made half 1/2" and half 3/4", it produces the same output whether or not the flow is going in one direction or the other; this illustrates the principle that the effect of the reduction is a linear sum. The sum of the reductions, of the 3/4" pipe and the 1/2" pipe. Both have their friction and both reduce flow over the distance. I repeat that having a 3/4" pipe at the tail end is still a good thing just as it would be if you had a longer 3/4" pipe way back before the reduction in size occurs.

    Still may not give you the hoped-for result. How many jets? How many might run all simultaneously? How much is house water pressure? How long is the run of 1/2" pipe? I mean from the initial point of reduction up to the point where you are hoping to increase size to 3/4".

    david
    Last edited by geniescience; 12-12-2006 at 04:57 PM.

  5. #5

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    Thanks for the insight...sounds like a math word problem! To answer your questions:

    How many jets?

    4

    How many might run all simultaneously?

    4 and the main shower

    How much is house water pressure?

    Not sure but want to measure it. Any inexpensive device that would do so?

    How long is the run of 1/2" pipe?

    It's about 5-6 feet from where it tees off from the 3/4" pipe.

  6. #6
    Retired Defense Industry Engineer jadnashua's Avatar
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    Default

    A normal "main" showerhead is rated at 2.5 gallons/minute. The jets can be anywhere from that down to about 0.8gallons. If they are max, then you're talking 12.5 gallons/minute. This is likely more water than a 0.5" pipe will comfortably supply, not counting a valve that can flow that much. You'd probably need a valve with 3/4" supply lines, and going from 0.5" to 0.75" won't improve the volume.

    This is also a thing to consider - at 10-12 gallons/minute, how big of a water heater do you have? It will need to be huge, or you'll only get about 3-4 minutes before it gets cold! Consider a thermostatic shower valve, at least then, you'd be able to keep going with one temp until it gets cold.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  7. #7
    Homeowner geniescience's Avatar
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    Default jet maker will tell you how many GpM you need.

    after you find out how many gpm in total, you'll know how bad it'll be to have left the 1/2" pipe. Hope it's just as easy to put a new 3/4" tee and slide a new 3/4" pipe up to the bathroom. I would continue with 3/4" to every jet and shower head. Even if in some cases it was not explicitly necessary. I like big pipes.

    david

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