Steve said:
I think that energy efficiency is dependent upon volume of hot water used. If you use a lot regularly, I'm not so sure that it is actually more efficient.
Efficiency can rise as usage increases, but that's not saying cost goes down. It goes up. But you pay less per gallon. Imagine keeping a water heater going without ever turning on the hot water tap. That would have a cost to run with no benefit, so the efficiency is infinitely bad (division by zero). Let's say it costs $1/day hypothetically. Then you use one gallon per day, and let's say that costs $1.10. The second gallon might cost you another $0.08. The more you use, the more efficiency rises, but that's not saying you should run the hot water copiously just to improve your efficiency.
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