Our slab-built home in Central Florida was built 1958 and has badly corroded galvanized pipes. The pipes are in/under the slab and are not accessible for replacement. Three locations need hot water.
LOCATIONS: The 3 locations are built against outside walls, and each has a cold-water spigot located outside and within 3 feet of the required point-of-use. Each of these outdoor spigots is the termination on a pipe that "stand ups" a couple of feet out of the the ground and serves nothing else except occasional garden-hoses (ie: they are not mounted on the wall and appear not to be served by pipes from inside the house).
TEMPERATURES: The measured outdoor water temp coming into the house is 73 degrees, but 65 degrees is possible during the dead of winter (February). Our desired output water temperature is 110 degrees max (!) at each of the three locations.
TURN-ON FLOW: Our desired flow-requirement for the 'turn on' of hot water is 0.5 GPM (less is preferred) at each location.
MAX FLOW RATE: Two of the locations need a max flow rate between 1.5 - 2.5 GPM, but 1.0 - 1.5 GPM is the desired max flow rate for the other location.
POWER: The house has no gas service of any kind, and I will not install gas. Electric service is 200 AMP and I have 10 vacant slots available in the breaker-box.
WIRING: Due to previous-owner changes, one location already has an unused AWG12-2 (and bare ground-wire) cable available under that bathroom's vanity, and I have already tested it and found it usable. One location must be wired during current work (we are re-siding). The remaining location will either be wired during current work or will be put off until more funding is certain.
SALVAGE: When these point-of-use tankless electric water heaters have been installed the present 40 gallon heater will be removed and offered on freecycle.com; its under/in-slab piping will be abandoned.
HELP WANTED: Advice will be appreciated, especially advice about wiring and breaker sizing, about siting the units, about our expectations (described beside the capitalized headings, above), and (especially) about reliable brands, and (also especially) about service and satisfaction experience.