Rick,

Electric water heater efficiency is 3.413 BTU/Watt. That conversion
factor does not change with age of the heater. If the power is going
in the heat ends up in the water. It has nowhere else to go! With a
gas water heater, there are flue losses, some of the heat goes into the
water and some goes up the flue. As a gas water heater ages, soot and
corrosion and lime build up on the heat exchange surfaces; then more
heat goes up the flue & less into the water, so the efficiency drops.

As for warranties, my brother is a full time plumber. He commonly
sells tanks with 8-10 year warranties. Look around.


Stretch