"RF" wrote in message
Electricity is used ONLY when the water is running. Even if it costs more
than
gas per thermal unit , it should still cost less overall. At present there
are losses from the existing tank in an uninsulated garage 24 hours/day
and 30' of copper piping (with R-6 insulation) when the water is running.

That may or may not be entirely true. In our area electric rates are about
17¢, about twice the cost of gas for the same energy. After considering the
cost to buy, install, and get enough power to the unit, that gas becomes
very reasonably priced here. Just take everything into consideration,
including the cost of getting power to that electric heater.