A. O. SMITH TK-310U-I 2**

The registry lists this model with a UEF, the ratio of hot water delivered to energy used, of 0.81. This site combined that value with the DOE test's daily hot-water draw for the high draw pattern to reach 209 therms of natural gas a year. The registry does not publish that annual figure, so it is a site calculation from DOE CCD data retrieved on 2026-09-19. Among the 397 models registered as a gas tankless unit at this draw pattern, this one has the 323rd lowest energy use. The class median is 182 therms, so the gap of 27 therms is measured at the test draw, not in any particular home.

A high draw pattern describes a larger household, or one where showers and laundry overlap. This model is listed at that pattern with a maximum flow rate in gallons per minute of 4.7. It fits a reader whose household matches that description and who has already settled on a gas tankless unit. It fits less well a reader whose main concern is low gas use. At 209 therms, the model sits 27 therms above the 182 therms median, and the models ranked ahead of it in the class register lower energy use at the same draw. To compare other options, use the selector by fuel, space and size or find a same-class replacement by model number.

The running cost is not stated here because it depends on your state's average residential gas price, which this text does not assume. The 209 therms figure is the quantity that price applies to, and the 27 therms gap to the class median converts to a cost difference at the same rate. The cost calculator on your own ZIP applies your rate to this model's annual energy use. The steps behind that calculation are in how the annual cost is calculated. Your actual gas use is not available from the registry, because the figure above reflects the federal test draw only.