Dilemma over using 3/4 vs 1/2

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yannick

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Hi,

I'm replumbing a part of the house in copper 3/4 and 1/2.
Usually I go 1/2 for the pipes leading to faucets and 3/4 for the "carrier pipes" (the ones connected to the main water and water heater) across the house.

One thing I wonder though. Under my kitchen sink there's the 3/8 dishwasher flexible pipe that connects to the hot, and it connects to the same pipe that brings water to the kitchen faucet. In other words, the copper pipe will be divided into two, one going to the dishwasher, one going to the kitchen faucet.

Should the copper pipe be 3/4" that divides into 1/2(faucet) and 1/2(dishwasher)?
Or would a 1/2 copper pipe that divides into 1/2(faucet) and 1/2(dishwasher) work equally well?

Since this pipe will be about 8 ft and before connecting to the "carrier pipes", I wonder if it's better to go 1/2 and have less heat loss and faster time before having hot water or go 3/4 for avoiding flow loss due to the fact it's divided, so when the dishwasher runs I suppose the flow will be reduced at the kitchen faucet.

A quick calculation of area tells me (1/2)^2 / (3/8)^2 = 1.78, so the cross sectional area of the 1/2 pipe isn't exactly twice the 3/8 pipe area.
Whether or not this accounts to much is a question I have for a plumber who definitely has more experience than me. I have other choices similar to this one to make down the line.
 

Fitter30

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1/2" is fine coming off 3/4". 120° flows 5 feet per second max 3 gpm. Since the kitchen faucet is pipes straight through the tee and dishwasher comes off the side outlet (bull). Faucet will get most of the water dishwasher might take a little longer to fill but a sink isn't running 100% hot water for a long time. Can find out how much a cycle uses it is in the specs.
 
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