A. O. SMITH TK-110U-I 2**

The registry lists a UEF, the ratio of hot water delivered to energy used, of 0.81 for this unit. This site combined that UEF with the daily hot-water draw the federal test uses for the medium draw pattern. The result is 137 therms of natural gas a year, and the registry does not publish that figure itself. The data comes from DOE CCD, retrieved 2026-09-19. The medium draw pattern describes a typical three- or four-person household. The maximum flow rate in gallons per minute is 3.5. The flow rating is listed separately and does not enter the annual energy calculation.

Among the 80 models registered as a gas tankless unit at the medium draw pattern, the median is 135 therms a year. This unit uses 137 therms, which is 2 therms above that median. It ranks 52nd lowest in energy use of 80. That places it in the second-highest quarter of its class for energy use. The comparison suits a reader checking this model against others at the medium draw pattern. It does not cover a household whose hot-water use differs from that pattern. No figure for another draw pattern is available on this page.

Running cost depends on the state average residential gas price, so this page does not state it in the text. Apply your own gas rate to 137 therms, or enter your ZIP in the cost calculator. The method for calculating the annual cost is documented separately. The energy figure is fixed by the medium draw pattern and the UEF of 0.81, so only the rate changes the cost. The modeled installed-cost range appears in its own block with its source and date; it is not a quote. To check a same-class alternative, find a replacement by model number and compare it with the 135 therms class median.