A. O. SMITH ATM-180M-N 1**

The figure of 178 therms 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 0.95 with the DOE test's daily hot-water draw for the high draw pattern. The source is DOE CCD, retrieved 2026-09-19. The registry also lists a maximum flow rate in gallons per minute of 5.4. That rating is separate from the annual figure, which is based only on the UEF and the test draw. The figure applies to the federal test's daily draw and to natural gas. A home that draws more or less hot water than the test will use a different amount of gas.

Among the 397 models registered as a gas tankless unit at the high draw pattern, this unit has the 45th lowest energy use. That places it in the lowest quarter of its class. Its 178 therms sits 4 therms below the class median of 182 therms, measured at the same draw pattern. The high draw pattern describes a larger household, or one where showers and laundry overlap, so this figure is relevant to a home with that kind of use. It does not describe a home with a different pattern, and this page gives no figure for one. A reader with a different pattern can start from the selector by fuel, space and size.

The running cost is not written in this text. It depends on the state average residential gas price for the reader's own state. The cost calculator on your own ZIP applies that price to 178 therms, and how the annual cost is calculated is documented separately. At any one gas price, the yearly gas difference from a median unit is 4 therms. Actual gas use of the A. O. SMITH ATM-180M-N 1** in a specific home is not available here. The modeled installed-cost range is shown in its own block with its source and date. It is a modeled range, not a quote.