Lennox WHGS040S40NANE****

It holds 38 gallons in the test, 2 gallons less than its 40-gallon sold size. Over one hour from a full tank, it gave 62 gallons in the test (its first-hour rating). That is 24 gallons more than its tank holds, since it reheats during the hour. Of 763 gas storage models, 671 give more hot water in the first hour. Among gas storage models, the median first-hour rating is 78 gallons.

As of Oct 26, 2026, it was not listed as ENERGY STAR certified. In tests, 60% of the energy it uses ends up as hot water (UEF 0.60). In the test, daily hot water use was set to medium (its draw pattern). Among 288 gas storage models on its draw pattern, 88 have a higher UEF. Its UEF is the median for its type and draw pattern. The water took in 78% of the energy used to reheat it (its recovery efficiency).

There are 2 more basic models with the same test figures. Those basic models are sold with AMERICAN STANDARD WATER HEATERS and Ariston as their brand names. For the full group, see the AMERICAN STANDARD WATER HEATERS GN40L2-3-* page.