Thoughts on downsizing pipe

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CDS

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Need some professional advice on a potential upcoming project.

I am looking to install a water softener. The main line into the house is 1" copper. My plan was to branch off with pex to the softener, and return to the main line, about 100' round trip. Would there be any issue with downsizing to 3/4" to and from the softener? I have city water, 2.5 baths, my water pressure is on the high side (80+), and I don't have any issues with drops during heavy demand.

Appreciate the help!
 

Jadnashua

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Not a good idea! The ID of 1" copper is very close to 1" (depends on the wall thickness), but 3/4" pex's ID is 0.681". Take the area of the copper opening (ID) = .25*pi , take the area of the pex = .116*pi, or only 46% of the area of the opening. Then, throw in the fact that adding 100' of pex will have a significant amount of friction in it as well, the pressure during high use would be significantly lower. Even 1" pex would be about 80% of the capacity of 1" copper. Throw in the possibility that you may need to add some fittings in there, and the pressure drop gets bigger still. To get equivalent volume and thus minimal pressure drop, you'd need to go to at least 1.25" pex.
 

Reach4

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Snipped from http://www.rehau.com/download/1334324/residential-pex-design-guide.pdf page 59. I think this is PEX B. Note that the softener and fittings will add some more drop. So maybe multiply the numbers in the table by 2.5.
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