water line size

Discussion in 'General Plumbing Help' started by chutch76, Feb 26, 2014.

  1. Feb 26, 2014 #1

    chutch76

    chutch76

    chutch76

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    Hello,

    I have a tankless water heater that requires a 3/4 supply line. I have noticed that my main line under the house is 3/4 copper but currently to my water heater it is reduced to 1/2 CPVC. I would like to change this to be correct because I am doing some renovations and have to move the lines anyway. So if I take somewhere off of the 1/2 CPVC and expand it up to 3/4 to the new position of the water heater I am not really doing any good. Is that correct? I assume once you neck it down to 1/2 you are reducing the amount of water to flow through the system. Going back to a 3/4 line will only make the flow rate slower?

    Thanks for the help
     
  2. Feb 26, 2014 #2

    phishfood

    phishfood

    phishfood

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    That is correct, it should be 3/4" throughout the run, until it reaches a point that no longer requires 3/4" for proper volume and pressure.
     
  3. Feb 26, 2014 #3

    chutch76

    chutch76

    chutch76

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    Thanks!

    So my next question is when running my water line to the shower should I run 3/4 all the way to the shower valve if I would like more velocity at the head? I think the valve is only a 1/2 so do I gain anything by running the 3/4 to it or should I just run 1/2 to it since that is what the valve is. I assume 3/4 would have less of a pressure drop since it is bigger but does that help my flow rate in the head? I think it would since you would be reducing a higher pressure down to a smaller area. The bigger the line going into the valve should equal a higher pressure at the valve therefore when it gets reduced the velocity should be higher. Am I thinking correctly?
     
  4. Feb 27, 2014 #4

    phishfood

    phishfood

    phishfood

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    Unless it is a long distance run with lots of fittings/changes of direction in between, you won't gain much at all by increasing the size. Remember, there will be two 1/2" lines feeding the valve, and only one 1/2" line leading to the tub spout or shower head. Most complaints of low pressure to a shower are either debris in the valve/head or a low quality/low volume shower head.
     
  5. Feb 27, 2014 #5

    chutch76

    chutch76

    chutch76

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    Really I won't be going to far. I have a small house and most of the runs will be a within 10 feet of the water heater with maybe a couple turns if any. Guess I will just run a 1/2 line to it then.

    Thanks again.
     

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