Electric resistance heat is 1.0 or 100% efficient, all electricity put into the heating element is converted to heat. Not sure if your trying to include power p

Electric resistance heat is 1.0 or 100% efficient, all electricity put into the heating element is converted to heat. Not sure if your trying to include power plant conversion and transmission losses, but that gets very complicated. Gas units range in efficiency based on how much heat they recover from the exhaust, 80% is typical, 90+ for a condensing heater with two stage heat recovery. The problem with condensing is the exhaust gases fall below condensation point for the water vapor created during combustion requiring a condensate drain complicating the install location and cost significantly. Heat pumps are over unity they use some energy to move more energy from the environment into the water, they are basically solar assisted resistance heaters. The energy cost difference is not as clear when comparing a heat pump tank storage unit to a gas on demand tankless they are both typically more cost effective than tank storage electric or gas. I have a 80% efficient tankless natural gas, it is wonderful having endless hot water at all faucets concurrently with a family of 4 plus occasional guests. I wanted to go condensing 90+ efficient but it was to complex based on its install location.