Ruud PROG40S-36N RH67 PV

The 171 therms figure is computed by this site, not taken from the registry. It combines the registry's UEF, the ratio of hot water delivered to energy used, with the DOE test's daily hot-water draw for the medium draw pattern. For this model the UEF is 0.65, from the DOE Compliance Certification Database retrieved 2026-09-19. The figure therefore describes gas use at the federal test's draw, not in any particular home. A household that draws more hot water each day will use more than 171 therms, and one that draws less will use less. How much more or less for a given household is not available from the registry data. The steps behind the calculation are set out in how the annual cost is calculated.

Within its class, the Ruud PROG40S-36N RH67 PV ranks 33rd lowest in energy use of the 288 gas tank models at the medium draw pattern. That places it in the lowest quarter of the class for energy use at the test draw. The tank's rated volume is 39 gallons. Its first hour rating, the gallons of hot water available in the first hour from a full tank, is 66 gallons. A home whose busiest hour stays within 66 gallons is close to the conditions this model was tested under. To set this unit beside others of a different fuel, space or size, use the water heater selector by fuel, space and size.

The 171 therms figure and the 33rd rank both hold only at the medium draw pattern. Energy use at a heavier or lighter daily draw is not available in the registry data used here. For a household that regularly needs more than 66 gallons in its busiest hour, neither number describes its likely use. The running cost is not written in this text, because it depends on your state's average residential gas price. The page computes it from your ZIP, applied to 171 therms of natural gas at the medium draw pattern. You can run the same figure in the cost calculator on your own ZIP. If you are matching this unit rather than checking it, you can find a same-class replacement by model number.