look for Energy Factor on box water heaters are packaged in.
Whirlpool makes a .95 energy factor.
water heater is larger due to higher insulation inside of unit.
additional savings can be added by externally insulating w/h
with w/h blanket.
as water heaters run 24/7 it is an item to spend the extra cost on for
the higher efficiency.
best of luck.
The cure of the part should not be attempted without the cure of the whole. ~Plato