RELIANCE WATER HEATERS GUF-40 1**

The registry lists a UEF, the ratio of hot water delivered to energy used, of 0.65 for this model. This site computed the 171 therms figure from that UEF and the DOE test's daily hot-water draw for the medium draw pattern. The registry does not publish the figure itself. The source is the DOE CCD, retrieved 2026-09-19. Among the 288 models registered as a gas tank at this draw pattern, this one ranks 33rd lowest of 288 in energy use, in the lowest quarter of its class. The gap to the 185 therms median is 14 therms. The figure holds only for the test draw. A household that draws more or less hot water will use a different amount, and that amount is not available here.

The first hour rating, the gallons of hot water available in the first hour from a full tank, is 68 gallons for this model. The rated volume is 38 gallons. A household whose busiest hour stays within 68 gallons matches the medium draw pattern the energy figure was computed for. A household whose peak hour exceeds 68 gallons is not covered by this figure, and the registry does not say how such use would change the energy total. The 33rd lowest rank says nothing about capacity. To compare size and space against other gas tanks, use the selector by fuel, space and size, or find a same-class replacement by model number.

The running cost is not written here because it depends on your state's average residential gas price. It is that price applied to the 171 therms at the medium draw pattern. The 14 therms gap below the 185 therms class median scales with the same price, so its cost effect also depends on your rate. The cost calculator on your own ZIP computes both from your location. The steps are described in how the annual cost is calculated. The page shows a modeled installed-cost range in its own block, with its source and date. That range is a model, not a quote, and it is not repeated in this text.