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Thread: 3/4 inch supply line to master bath, but 1/2 inch line at shower valve?

  1. #1
    DIY Junior Member barbourdg's Avatar
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    Default 3/4 inch supply line to master bath, but 1/2 inch line at shower valve?

    Need some help with our bathroom remodel.

    We have 3/4 supply lines coming into the master bathroom (sink and shower) and about 5 feet of 1/2 inch to the bathtub. We are doing a complete remodel and the bathtub 1/2 line is closest to the new shower location. We are installing a Kohler Water tile Rain Head, 3 body sprays and hand shower.

    So what makes more sense.

    1. Use the 1/2 inch line with a 1/2 inch valve
    2. Use the 1/2 inch line, but with a 3/4 inch valve
    2. Cap off the 1/2 inch line and reroute one of the 3/4 supply lines to the valve?

    The system would never have more then 2 devices running at the same time, plus we have a 60 gallon water heater. So we don't want a 5 minute shower either.

    Thanks for the advice!

  2. #2

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    Whats your water pressure run?

  3. #3
    DIY Junior Member barbourdg's Avatar
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    From what I hear my city averages about 60 PSI.

  4. #4

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    What kinda volume are we looking at per body spray??? The handheld and the rainhead are suppose to be limited to 2.5 gal per minute at 80 psi I believe. We need to calculate how much water you will be needing with two functions in use.
    Most 1/2" shower valves will run over 7 or 8 gallons a minute.

    Check the specs on the 1/2 valve and see what it will flow with the 60 psi you have compared to the total of the gallons your two functions will use.

  5. #5
    DIY Junior Member barbourdg's Avatar
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    We haven't bought the valves yet, but here are the options:

    Pressure Balancing Valve (Rite-Temp)
    3/4 Valve - 13.0 gpm
    1/2 Valve - 5.0 gpm

    or

    Thermostatic Valves (Master Shower)
    3/4 Valve - 17.2 gpm
    1/2 Valve - 10.9 gpm

  6. #6

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    I would use the 1/2" thermostatic.

  7. #7
    Retired Defense Industry Engineer jadnashua's Avatar
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    It depends on how many of those things you want to run at once! Unless your hot water supply is hotter than normally allowed (that's 120-degrees), you'll be using mostly hot water, especially in winter when the incoming supply water is (often) much colder, a 1/2" valve would be hard pressed to deliver those specs within the safe flow velocity of the water pipes (about 5pfs). Faster water flow creates turbulence, noise, and can literally create holes in the piping after time.

    You need to look at the specs of the individual sprays you want to run at once. Add them up. Four body sprays by themselves could run anywhere from 2-10gpm depending on their design. Then, add one other showerhead, and you've overloaded the system, and the performance will be lousy.
    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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    DIY Junior Member barbourdg's Avatar
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    The Kohler body sprays are 2.5 gpm, we're installing either 2 or 3. We would only have them going with one other device at the same time.

    Since all the main lines are 3/4 to the bathroom, do you think 4-5 feet of 1/2 would hurt the pressure that much? If we bumped the 1/2 inch line back to 3/4 before the valve?

    We can reroute another 3/4, but it would take time and be a little tricky. But doable

    Thanks for all the info guys!

  9. #9

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    Quote Originally Posted by barbourdg View Post
    The Kohler body sprays are 2.5 gpm, we're installing either 2 or 3. We would only have them going with one other device at the same time.

    Since all the main lines are 3/4 to the bathroom, do you think 4-5 feet of 1/2 would hurt the pressure that much? If we bumped the 1/2 inch line back to 3/4 before the valve?

    We can reroute another 3/4, but it would take time and be a little tricky. But doable

    Thanks for all the info guys!
    Running 3 body sprays plus another function would put you at 10 gpm. If you had a hot water temp setting of 120 degrees and a cold incoming water temp of 60 degrees and a mixed shower temp of 105 degrees you would be using 75% hot water.

    You would get about 5 minute shower at 105 degrees running 10 gpm. assuming the water heater had its full capacity of storage at the time you wanted a shower.

    If you had a hot water temp of 140 degrees and a incoming water temp of 60 degrees with a shower temp of 105 degrees you would be using 56% hot water to achieve that ratio. Your shower would last roughly 20% longer......thats not much.

    You stated you have a 60 gal heater.

    I can already tell you your water heater is undersized for what you have planned.

    For 3 bodysprays running 2.5 gpm each and another function of 2.5 gpm I would use the 3/4 valve and run 3/4 piping to it for sure. If you did 2 body sprays plus another function totaling 7.5 gpm I would use the 1/2 thermostatic. and leave the piping alone.

    Consider installing two 50 gal water heaters in parallel set at 140 degrees with a tempering valve set at 125. Fly me over to Texas to supervise the job. LOL
    Last edited by Hackneyplumbing; 02-12-2013 at 09:18 PM.

  10. #10
    DIY Junior Member barbourdg's Avatar
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    We were actually thinking about getting a new water heater anyway, so we can upgrade.
    Thanks

  11. #11

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    The bodysprays are rated usually at 80 psi. Kohler doesn't list the pressure but lists the volume at 2.5 gpm. If you have 60 psi at the meter you will have some pressure loss by the time you get the water to the bodysprays because of friction through the pipe,fittings and valves.

    You would get 75% of the listed volume with 60 psi, That calculates out to 1.875 gpm. Multiply times 3 for the bodysprays and you get 5.625 gpm. Now figure in a little pressure loss and you would at best be getting 5 gpm out of all 3 bodysprays. Now add another 1.875 for the second function minus some pressure loss through the piping and you would get about 1.5 gpm. Total your going to be running about 6 to 7 gpm.

    Thats unless you remove flow restrictors.......thats illegal tho. No one really does that do they??? LOL

  12. #12
    DIY Junior Member barbourdg's Avatar
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    Sounds like I should go with the 1/2 Thermostatic Valve, and just limit my shower to 2 body sprays and one other device running at the same time.

    Thanks

  13. #13
    Moderator & Master Plumber hj's Avatar
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    As a practical matter, if you compute the actual size of the openings in a 3/4 valve, you will find that a 1/2" a pipe has the same, or almost the same, area, so you can use any of your options and have the same results.
    Licensed residential and commercial plumber

  14. #14
    DIY Junior Member barbourdg's Avatar
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    Just checked with the city, and our PSI averages between 65 to 85. Since we live right by a pump station and a ground level water tower, they think it's pretty high. They're sending somebody by this afternoon or in the morning, to measure it.

    Would that matter, if I have 80 PSI? If we went with the 1/2 valve? Any benefits of piping the 1/2 into a 3/4 valve?
    Last edited by barbourdg; 02-13-2013 at 08:31 AM.

  15. #15
    Plumber jimbo's Avatar
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    A 60 gallon WH will deliver, round numbers, close to 45 gallons of shower-temp water. At 15 gpm for all those sprays, that will be a 3 minute shower.

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