I believe a standard gas water heater is about 78% efficient, for a net gain of 18%. It does generate condensate, but since my gas furnace is near by I was abl

I believe a standard gas water heater is about 78% efficient, for a net gain of 18%. It does generate condensate, but since my gas furnace is near by I was able to set it up to use the same drainage system. The unit was about $2500, versus probably something like $1000 for a more "standard" power vent unit. So $1500 to make up, worst case. It burns 100,000 BTU an hour when it runs. A gallon of propane is about 91,500 BTU. So every hour is around 1.1 gallons of propane. The unit has run for 1368 hours so far, resulting in it consuming around 1505 gallons of propane. Assuming I would have used 18% more propane for a regular heater, that would mean 271 gallons saved. Propane cost fluctuates a lot here, but if we just run with a $2.50/gallon average, then it has saved me something like $678. There are a bunch of things I don't know though. For example, I don't know if this unit retains the heated water better than their lower/standard ones. I suspect it does given how infrequently it runs. It's design is also supposed to maintain its efficiency as it ages versus losses from a "standard" burner setup. True story or marketing shenanigans, I don't know. I was able to take advantage of a government program at the time to get a tax incentive on the heater due to its efficiency. I don't remember the exact amount, but I'm likely about even on it now between the incentive and the recoup. But, discarding that, I'd be about 50% recouped and have had a great hot water experience. It just never runs out, it rarely runs when there isn't an active draw, it only operates for minutes when it does run, it's LCD/metrics scratch my geek itch, and it's probably the best I can do for the environment given my constraints.