A. O. SMITH ATO-140B-N 1**

The figure of 137 therms a year is computed by this site, not by the registry. It combines the registry's UEF, the ratio of hot water delivered to energy used, of 0.81 with the daily hot-water draw DOE assigns to the medium pattern, which represents a typical household on a busy morning. It applies to natural gas only and to that draw pattern only. A household that draws more or less hot water than the test assumes will use a different amount. The source is DOE CCD, retrieved 2026-09-19. The maximum flow rate in gallons per minute is 3.6; that is a capacity rating and is not part of this energy calculation.

Against its class, the unit ranks 52nd lowest energy use of 80 models, in the second-highest quarter of its class for energy use. Its 137 therms is 2 therms above the class median of 135 therms. The comparison covers only gas tankless models registered at the medium draw pattern and says nothing about other heater types. It suits a household that matches that draw pattern and accepts energy use above the class median. It suits less well a reader whose priority is low energy use, since this unit sits above the median. To check alternatives, use the same-class replacement finder by model number or the water heater selector by fuel, space and size.

The running cost is not stated here because it depends on your state's average residential gas price, and this page assumes no rate. Multiply 137 therms by your own price per therm for a first check, or enter your ZIP in the cost calculator. The result stays tied to the medium draw pattern; a household with different hot-water use will see a different bill. How the annual cost is calculated is explained on the methodology page. The modeled installed-cost range appears in its own block with its source and date and is not a quote.