U.S. Craftmaster GUC 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 83 gallons in the test (its first-hour rating). Reheating lets it give 45 gallons beyond the 38 gallons in its tank. Of 763 gas storage models, 242 give more hot water in the first hour. The median gas storage model gives 78 gallons in its first hour.

As of Oct 26, 2026, it was not listed as ENERGY STAR certified. In tests, 64% of the energy went to hot water, so its UEF is 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. On its draw pattern, the median gas storage UEF is 0.66. The water took in 74% of the energy used to reheat it (its recovery efficiency).

It is the basic model for UNG1F4040TR 4**, UNG1H4040TR 4**, and UNG1J4040TR 4**. All of its test figures are shared by 8 other basic models. Between them, those basic models carry 4 other brand names. You can find the whole group on the page for the A. O. Smith G6N-UT4040NVR 5**.