Thanks for the replies. As far as the individual models, I'm afraid that may get too pricey. I'm almost done with this project and I'd have to run 240 circuits to
these locations. This is an historic building and I don't have cabinetry to hide things in (pedestal sinks) so equipment in the bath isn't feasible. I do have easy access in the basement under the first floor baths, but its not heated down there. I will point out that all the lavs, regardless of which floor they are on are fairly centrally located and all at the middle to rear of the building.
I'm starting to wonder if using a traditional tank (30 or 40 gal?) and putting it on a timer to turn down at night, and even setting the max. temp to hand washing levels as opposed to shower levels makes good sense?
The Bosch Ariston series mini tanks all run on 15A 120V service (either plug outlet or hard-wired). But if it's all truly centrally located and a single tank can be located directly beneath the vertical runs to minimize distribution lengths a single tank might be the right solution.
If it's actually cold down there (under 60F), insulating all of the basement plumbing to at least R6 (including the nearest 6' of the cold feed, and the pressure/temperature valve outlet) puts a big dent in the standby losses, as does going with at least an R20 tank (or bringing it up to over R20 with an extra blanket.) Setting the outlet temp to the minimum-legal value is also a standby saver. (If, as in some locations, you're required to maintain 140F+, maybe a small tankless IS the right way to go.) If it's ~65F or higher in the basement on average, R4 on all of the plumbing would be still be cost effective. (You can get suitable closed cell pipe insulation at Grainger, if you don't have another source. Box stores tend to only carry R2.)
Also, smaller/fatter tanks are (all else being equal) less lossy than taller skinnier tanks- the surface-area/R-value issue. Depending on your actual peak hour HW usage (which may be difficult to determine), you might get away with an 8-10 gallon mini-tank and insulate the hell out of it, but if it's not enough, there are options. In general, smaller tends to be slightly more efficient than larger- go 30 gallon, not 40 or 50. Since your volume use is low (nobody taking showers), you can probably go with a 120V version if you go as big as 20-30 gallons, since recovery times can be long without consequence. A 30-gallon shorty/compact would have minimal surface area losses and plenty of capacity, and under 50W standby if insulated to R20 with near-tank plumbing at R4. (Figure ~350-500kwh/year in standby loss.) Look for something small, easy to insulate, with an EF of .93+ (eg Rheem 82VP30-1, but there are many others.) Most are available in 120V 1500-2000W versions.
Turning off electric tanks at night with timers yields vanishingly small savings, since standby losses are low, and well over 90% of the electricity you didn't use overnight you end up using to bring it up to temp in the morning. The standby losses don't drop significantly until the tank is 10s of degrees F cooler, and in 12 hours a 130F tank might cool off to maybe 122-125F (depending on how cold the room is), not 105F (unless it's outdoors, in January, in Maine). You'd save at most $8-10/year with a timer even in high electricity rate areas, probably less where you are.
