recirculation? or separate point of use. >75 feet.

[Matt Rademacher]

The Rinnai tankless will be more than 75 feet from the kitchen. (DW heats it's own water)

1. instead of running a recirculation loop, and keeping that line warm, could I just run cold and use a separate, point of use heater, under the cabinet?

2. and is 1/2" pex fine for that distance for sufficient flow.

thanks a lot!

 

[Jadnashua]

A typical sink faucet is flow restricted, and a 1/2" pex should be able to supply more volume than it can flow. At that distance, you will see some dynamic (water flowing) pressure drop. One calculator I tried said that on a 75' run of 1/2" pex with no couplings, the pressure drop at 2.5gpm (higher than the spec allows for a faucet but a little) was 7 psi. With a 3/4" run, the pressure drop changed to 1.4 psi...so, it would be better if you ran that in 3/4", but 1/2" would still probably work for you, depending on the normal water pressure in the house.

 

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[Matt Rademacher]

Great info...
I'll choose the 3/4 since we have a tank on the hill and have only decent pressure.
I'll use the rest of the 3/4 to serve the tub, but since everything else is less than half that distance, I'll go with 1/2.
Thanks!

And, the more I think about it, I'll bring just cold the 75' and install a point of use heater at the kitchen sink...

A typical sink faucet is flow restricted, and a 1/2" pex should be able to supply more volume than it can flow. At that distance, you will see some dynamic (water flowing) pressure drop. One calculator I tried said that on a 75' run of 1/2" pex with no couplings, the pressure drop at 2.5gpm (higher than the spec allows for a faucet but a little) was 7 psi. With a 3/4" run, the pressure drop changed to 1.4 psi...so, it would be better if you ran that in 3/4", but 1/2" would still probably work for you, depending on the normal water pressure in the house.