CPVC vs Copper for Tub and Shower - GPM

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bnymbill

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Similar threads have been created but I haven't found the exact answer to my question. I understand that CPVC and copper have the same OD but copper has a larger ID which is why Kohler requires 1/2" copper for the tub supply from the diverter; otherwise water could be forced out of the shower head. My question is, since the Kohler Georgeson has a max flow rate of 2 GPM, why wouldn't 1/2" CPVC be sufficient? In other words, if the flow is restricted to 2 GPM by the diverter, how could it not force 2 GPM through CPVC? Obviously, I'm missing something. In the past, 1/2" copper worked for showers that flowed at 4 or 5 GPM. Thank you in advance!
 

Jadnashua

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CPVC would only work properly if you were doing shower only. The tub spout is not generally flow restricted, and usually is connected to the larger port of the valve (assuming it will let you use two, not all do). Are you using the diverter in the tub spout, or a separate one?
 

Terry

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The Kohler instructions
IMPORTANT! Do not use multiple elbows on the bath spout outlet. Use 1/2″ NPT threaded adapters or solder 1/2″ copper directly to the outlet.

CPVC does not work with the Kohler K-304 valve. Or with Moen, or with Delta.
It will force water up to the shower head while filling the tub.

https://terrylove.com/forums/index....hler-rite-temp-bath-shower-valve-k-304.41581/

k-304-r02.jpg


If I use pipe nipples, I get brass, not galvanized.
 
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bnymbill

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If I understand correctly, the flow to the tub spout is not restricted to 2 GPM, only the flow to the shower head is restricted. That makes sense as to why the volume restriction is an issue with CPVC.
 
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