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I am installing a new shower system (3/4") - the main is 3/4" but splits immediately into 1/2" cold and 1/2" to the hot water heater. I'm thinking I need to re-plumb all the way back to the 3/4" copper main.

The question is should I go with 1" pex, or 3/4" pex. I know it's counter intuitive to go from 3/4" copper main to 1" pex, but I thought I read somewhere that pex actually has a smaller inside diameter and a lower flow rate. I'm thinking by going 1" pex down the center of the house (where everything feeds from), I won't have water pressure issues later on. I'll tee off all the old feeds into the 1/2" existing copper.

The shower will have a rain shower, two hand helds and 4 body wash jets - so will pull quite a bit of water) although likely they will not all be on at the same time).

Any thoughts?
 

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Civil Engineer
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PEX is slightly less rough than copper, therefore the difference in inside diameter typically makes little or no difference to effective flow rate. You can use 3/4 inch PEX or 3/4 inch copper, makes no difference to the total flow.
 

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flipping slumlord
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I know it's counter intuitive to go from 3/4" copper main to 1" pex, but...

...the main is 3/4" but splits immediately into 1/2" cold and 1/2" to the hot water heater. I'm thinking I need to re-plumb all the way back to the 3/4" copper main.
If you have 3/4" copper water service then you should maintain that throughout the house (as the primary material and size) including into and out of the water heater.

When you get to fitting tees for the several fixture you can reduce to 1/2" for most.

I am installing a new shower system...
The shower will have a rain shower, two hand helds and 4 body wash jets - so will pull quite a bit of water... Any thoughts?
Mostly that it seems a silly and wasteful indulgence. As to the plumbing work needed... whatever size fittings the MIXING VALVE calls for is what I'd connect to it.

hth
 
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