PEX-A Whole-home Repipe - Sizing Advice

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Joe Weekley

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Planning a 2nd floor bathroom remodel and will be taking the opportunity to replace the 65 year old copper with PEX-A in the whole house while I'm at it. Decided on trunk & branch (vs home-run) and wanted to solicit some advice/opinions on sizing.

Attached is the current layout. 3/4" copper supply into the house, switching to 1/2" copper at the water heater. Current trunk and all branches are 1/2" copper. Water heater and all 3/4" from the main shut off was replaced in Dec 2017. Will be using Sioux Chief PEX-A from Menards.

House is 1800 sq ft, two floors with unfinished basement, 2 baths (1st floor, 2nd floor). Laundry sink and washer are in the basement. Water heater location is fixed and on the opposite side of house from the washer 30 ft away. Static water pressure is 75 psi in the basement. Longest current hot run is 50 feet (2nd fl lav) and takes about 38s to get hot water. 1st fl bath lines run through the main basement wall into a crawlspace.

Plan is to transition to PEX at the water heater and trunk with individual 1/2" drops to the fixtures and branches (drop to sub-group) to the two bathroom groups where I'll feed a multi-port tee/manifold then 1/2" drops. 2nd floor bath is primary and will have a tub/shower combo (90% of the time shower only). 1st floor bath has a jetted tub that is seldom used, OK with current fill time (though could be better). I'm trying to determine what sizing would be best for this and can think of four options

1. 1/2" trunk, 1/2" branches and drops. (Essentially what I have now, except the ID difference between PEX and copper.)
2. 3/4" trunk, 1/2" branches and drops.
3. 3/4" trunk, 3/4" branches to bathroom groups, 1/2" drops to individual fixtures
4. Upsize to 1" trunk, 3/4" branches to bathroom groups, 1/2" drops to fixtures (these seems like overkill and would waste a lot of time/water waiting for hot to arrive. 2nd floor bath run would be 40+ feet)

Does mixing hot/cold sizes offer any benefits or concerns with balancing? Say 3/4" cold and 1/2" hot? Hot Water Recirc isn't in the plans currently, but a possibility in the future if family grows (only me and the wife currently).

Appreciate any advice!

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NMP

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Looks like you've done lots of research so far. I'd be curious what others thought as well. Have you completed the project yet?
 
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