PEX Sizing - Reduce from 1" to 3/4" at Water Heater and back up to 1" + Design Critique

[PBJ918]

I know there are a ton of threads regarding the subject of PEX sizing, but I couldn't find anything addressing this matter.
We're doing an addition and complete renovation on our house and I'm designing the plumbing using the PEX/Plumbing Logic method.

I wanted to start a 1-1/2" meter and service line, which is probably overkill and I'll just end up going to a 1" meter and service line (Cost is probably the underlining factor, but I will not get any meter size smaller than 1-inch). This goes to a 199,900 BTU tankless water heater with an internal circulation pump.

The inlet and outlet to the water heater is 3/4" and I designed the hot to jump back up to 1". Is this OK? Will I still improve the volume by doing this or will it become a choking point and we'll experience a large disparity between hot and cold?

I've attached the layout. Any feedback is welcomed.

NOTE: There is no fire suppression system.

 

[Reach4]

There is no problem having bigger service lines than the meter size. This is common, and is often a good idea or even mandatory to have bigger service lines to the house. There is no problem with a 1 inch or so line reducing down to the 3/4 inch water heater input.

You may want to avoid increasing the output of the water heater back up to 1 inch in that the 1 inch will hold more water, so will slow the arrival of hot water at the far end.

Also note that the ID of a 3/4 water heater nipple is significantly larger than the ID of a 3/4 inch pex pipe or fitting.

The pressure loss of flowing water adds up over various sections. A loss at a meter or water heater does not eliminate the benefit of bigger pipes in or out.

Looking at your diagram, I would opt for the cheaper 3/4 inch meter, and maybe upsize to 1 inch -- presuming that you don't have anything that needs unusually large flows. If you have a fire sprinkler system, then let the fire system designers guide you. I am not a plumber.

 

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[Terry]

IPC PEX chart for meter and distance
For most three bath homes a 3/4" meter is plenty. Upgrading to a 1" meter is a big improvement if you also changing the water service to 1.25" or larger.