Looking at Rheem water heater specs, I noticed some strange numbers. Two of their water heaters have all the same specs except for the warranty and the cost per year. The cost per year of one is $309 and the other is $231. Everything else is the same, including first hour rating, tank size, input btu/h, recovery rating, dimensions, weight, and energy factor.
I thought you could calculate the cost per year from the first hour rating, the btu/h input, the recovery rating, and the energy factor. But if all four of those are the same, how are they getting such different costs per year for them?
22V40F1, $309/year: http://waterheating.rheem.com/content/resources/documents/specsheets/Reside ntial%20Gas/RHGasFury.pdf
22V40 PROF, $231/year: http://waterheating.rheem.com/content/resources/documents/specsheets/Reside ntial%20Gas/RHGasPro.pdf