Lennox WHGS040S37NAXE****

The registry lists a UEF, the ratio of hot water delivered to energy used, of 0.6 for this model. This site combined that value with the DOE test's daily hot-water draw for the medium pattern to compute 185 therms of natural gas per year. The registry does not publish that annual figure itself. The source is DOE CCD, retrieved 2026-09-19. The figure applies only to the medium draw pattern, which represents a typical household on a busy morning. A household that draws more or less hot water than the test will use a different amount, and this page has no value for other patterns. The class median for the 288 gas tank models at this pattern is 185 therms, so this unit sits 0 therms from it.

Among the 288 models in its class, this unit ranks 89th lowest for energy use, which places it in the second-lowest quarter. Its first hour rating, the gallons of hot water available in the first hour from a full tank, is 64 gallons, and its rated volume is 38 gallons. The energy figure was computed for the medium draw pattern, so it fits households whose morning demand resembles that load. It does not show energy use under a heavier or lighter load, and the data here does not cover those cases. To compare other fuels, space limits or tank sizes, use the water heater selector.

The running cost is not written here because it depends on your state's average residential gas price, which is not part of this data. Enter your ZIP in the cost calculator to apply your own rate to 185 therms. The methodology page explains how the annual cost is calculated. The modeled installed-cost range appears in its own block on this page with its source and date. Because this model's energy use is 0 therms from the class median of 185 therms, a class-median model would use the same therms per year at the medium draw pattern. To look for a same-class option, use the replacement finder by model number.