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

The registry lists this model at a UEF, the ratio of hot water delivered to energy used, of 0.81, with a maximum flow rate in gallons per minute of 3.6. This site combined the registry's UEF with the DOE test's daily hot-water draw for the medium draw pattern. The result is 137 therms of natural gas a year. The registry does not publish that annual figure itself. The source is DOE CCD, retrieved 2026-09-19. The figure applies only to the test draw, so a household that uses more or less hot water will use more or less gas. The method is set out in how the annual cost is calculated.

Among the 80 models registered as a gas tankless unit at the medium draw pattern, this one ranks 52nd lowest for energy use. Its 137 therms is 2 therms above the class median of 135 therms, which places it in the second-highest quarter of its class. That gap is measured at the test draw only, and the registry data here does not show how it changes at other draws. A reader whose priority is the lowest gas use at this draw pattern will find models with lower use in the same class. A reader who has already chosen this unit can confirm that its figure sits 2 therms from the median. To compare within the class, find a same-class replacement by model number or use the water heater selector to filter by fuel, space and size.

The registry gives no running cost for this model, and this page does not state one in the text. The cost depends on your state's average residential gas price. Take the 137 therms at the medium draw pattern and apply your own rate per therm to get the yearly gas cost for that draw. Annual energy for other draw patterns is not available in this data, so no running cost can be worked out for a household with different hot-water use. The energy figure was retrieved from DOE CCD on 2026-09-19. The cost calculator on your own ZIP computes the running cost from your state's rate. The modeled installed-cost range is shown in its own block, with its source and date, and is not repeated here.