American GCB-40 4**

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 78 gallons in the test (its first-hour rating). That is 40 gallons more than its tank holds, since it reheats during the hour. Among 763 gas storage models, 366 have a higher first-hour rating. In first-hour rating, it ties the median gas storage model.

On Oct 26, 2026, this heater was not listed as ENERGY STAR certified. In tests, 64% of the energy it uses ends up as hot water (UEF 0.64). The daily hot water use in the test, called its draw pattern, was high. Its UEF is lower than that of 255 of the 434 gas storage models with its draw pattern. For its type and draw pattern, the UEF runs from 0.61 to 0.90. The water took in 77% of the energy used to reheat it (its recovery efficiency).

It is sold as GB61 40T40 4** and GB61 40T40 4*1. There are 5 more basic models with the same test figures. Each of the 5 other brands lists one of them. For the full group, see the A. O. Smith GCB-40 4**.