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Old 02-26-2014, 12:21 AM   #1
chutch76
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Default water line size

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



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Old 02-26-2014, 01:20 AM   #2
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.



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Old 02-26-2014, 02:51 AM   #3
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?

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Old 02-27-2014, 12:18 AM   #4
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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.

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Old 02-27-2014, 02:32 AM   #5
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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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