State GUC 40 4**

It holds 38 gallons in the test, 2 gallons less than its 40-gallon sold size. It delivers 83 gallons of hot water in the test's first hour. That is 45 gallons more than its tank holds, since it reheats during the hour. Of 763 gas storage models, 242 give more hot water in the first hour. The median gas storage model gives 78 gallons in the first hour of the test.

As of Oct 26, 2026, it was not listed as ENERGY STAR certified. In tests, 64% of the energy it uses ends up as hot water (UEF 0.64). Its test ran at the high level of daily hot water use. Of 434 gas storage models with the same draw pattern, 255 have a higher UEF. For its type and draw pattern, the median UEF is 0.66. When it reheats water in the test, 74% of the energy it uses ends up in the water.

Its 3 model numbers are GS 6 40 BRUT* 4**, GSX 40 BRUT* 4**, and GW8 40 BRUT* 4**. All of its test figures are shared by 8 other basic models. In all, 4 other brands list one or more of them. For the full group, see the A. O. Smith G6N-UT4040NVR 5** page.