A. O. SMITH ATI-180B-N 1**

This site computes the annual figure; the registry does not publish it. The calculation uses the registry's UEF, the ratio of hot water delivered to energy used, which is 0.82 for this model, and the DOE test's daily hot-water draw for the high draw pattern. The result is 206 therms of natural gas a year, from DOE CCD data retrieved 2026-09-19. The class median for the 397 gas tankless models at this draw pattern is 182 therms, so this model sits 24 therms above it. Its rank is 229th lowest energy use of 397, which places it in the second-highest quarter of its class for energy use.

The figure applies to one condition: the high draw pattern, which describes a larger household, or one where showers and laundry overlap. It is relevant to a reader whose household matches that description. A household that uses hot water differently would see a different annual figure, and this page does not give one for other draw patterns. The registry lists a maximum flow rate in gallons per minute of 4.7 for this model. Whether that flow covers several fixtures running at once depends on fixture flow rates and incoming water temperature, and neither is in the data. To compare units by fuel, space and size, use the water heater selector. For a same-class alternative, look up a replacement by model number.

The running cost is not stated here because it depends on your state's average residential gas price. Multiplying 206 therms by your local price per therm gives the yearly gas cost at the test's daily draw; actual bills will differ with real hot-water use. The cost calculator does this from your ZIP code, and the methodology page explains how the annual cost is calculated. Because this model uses 24 therms more than the class median of 182 therms, your gas price applies to a larger yearly quantity than it would for a median model. The installed-cost range appears in its own block on this page, as a modeled estimate rather than a quote.