Lennox WHGS040T40PAXS****

It holds 38 gallons in the test, 2 gallons less than its 40-gallon sold size. Starting full, it gives 74 gallons of hot water in its first hour of use. Reheating lets it give 36 gallons beyond the 38 gallons in its tank. Of 763 gas storage models, 466 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 went to hot water, so its UEF is 0.60. In the test, daily hot water use was set to medium (its draw pattern). Of 288 gas storage models with the same draw pattern, 88 have a higher UEF. On its draw pattern, its UEF is also the median gas storage UEF. Of the energy spent to reheat water, 79% goes into it (its recovery efficiency).

All of its test figures are shared by 3 other basic models. Those basic models are sold with AMERICAN STANDARD WATER HEATERS and Ariston as their brand names. You can find the whole group on the page for the AMERICAN STANDARD WATER HEATERS GSN40T1-3-*.