Water line replacement/upgrade to pex. Best way to hookup two different size hot water heaters

[Oconnellshawn88]

So this is in wisconsin and it is a duplex setup not currently rented and whole house is still used. So plumbing was done back probably in 70s and imo ran very inefficient and improperly. Am replacing all the waterlines to pex and are currently copper/steel. So ill layout my current plan and open to all input. Its city water which comes into softner except the line that goes to spicket and refrigerator. From the softner i plan to run to run to a checkvalve, then tee to a expansion tank, then use a bullnose T to a 50 and a 40 gallon electric heaters offset so that equal amount of pipe and distance is used measuring to the bottom of the water heaters. Then again at equal distance do the same merging then running to the fixtures in a main 3/4” line. Was planning on running 3/4” to both the wash machines but am having difficulty finding oxbox or similar and wash machine shutoff valves that accept 3/4” pex a expansion connection so probably end up just teeing off with 1/2” like rest of the home. So will then be 3/4x1/2x3/4 to the kitchen sinks, the bath vanities, lastly the shower will have 3/4x1/2x1/2 with return line to recirculate hot water which will tie in with a check valve and tee after the check valve from the softener and before the tee to the expansion tank. Some things i read say not to run parallel system with different size tanks tho. Bust then most sites say not to run in series anymore. What is the best/most cost and enegry efficient way. Fyi not currently worried about billing as duplex and if needed will just add a few cheap thread on water meters down the road that run to the fixtures to determine water usage to accurately divy up the bill unless someone knows a better way as well. Is a recirculating pump required or needed?Thoughts/advice/comments/concerns? Thanks

 

[Oconnellshawn88]

Also wondering about best ox box setups with water hammers, brand? Location?

 

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[Fitter30]

Are the waters used together or separately? If the two are feeding both spaces reverse return piping is needed.

Multiple Water Heaters: Reverse Return Piping Method - Water Heaters Installed by Licensed Plumber

In the evolving world of water heating technology, the reverse return, or ‘first in, last out’, configuration has emerged as a superior method for dual water heater setups. This approach not only improves efficiency but also offers notable flexibility and reliability. This is not the only way to...

kcwaterheater.com

If its a duplex why aren't there two meters? Why all the check valves? Every device water flow through there is pressure drop.

 

[Oconnellshawn88]

Theres 2 electric meters and panels. Not water meter tho. And when i say check valve i more/less mean backflow preventer. And yes i am having it return piped. But i dont want a recirculating pump cause from my understanding itll make water heaters run more and wear them out quicker and just intend on gravity fed recirculation from furthest fixture and parallel running of water heaters. My concerns are just making sure i split the load evenly and where to place expansion tank and valves/backflow preventers, also saw lot of people piping the return line into bottom of water heaters which i think is pretty dumb myself when if its mixed in with the coldest water before it even splits off to the tanks will be more efficient than having it mixing in multiple areas or thats my theory anyway. But i want to verify everything now so easier troubleshooting now than after install