I know that instantaneous water heaters are supposed to save energy.
The advertising says so.
The idea is that most of the energy used by conventional hot water systems is lost to storage radiation -- not withstanding any insulation.
I've never seen a bathroom rated instantaneous heater with less than (3) 40A double-pole 240V breakers.
In commercial settings, they have totally taken over: just a bathroom sink fed at 30A at 208V, 240V or 277V.
Heat pump driven hot water would seem to be a winner -- but I've only seen it done in Hawaii.
It should be as common as dust in Las Vegas!
