A. O. SMITH T-H3M-OS-N 1**

The 122 therms figure applies to natural gas at the medium draw pattern only, a typical three- or four-person household using hot water on a busy morning. It is not a value measured in the registry. This site computed it from the registry's UEF, the ratio of hot water delivered to energy used, and the DOE test's daily hot-water draw for that pattern. The registry lists a UEF of 0.91 for T-H3M-OS-N 1**. The energy source is DOE CCD, retrieved 2026-09-19. A household with a different daily draw would have a different annual figure, and this page has no values for the other draw patterns.

Among the 80 models registered as a gas tankless unit at the medium draw pattern, this unit ranks 4th lowest of 80 for energy use. That places it in the lowest quarter of its class, at 122 therms against a class median of 135 therms. The gap is 13 therms a year at the same draw pattern. The comparison suits a household whose use resembles the medium pattern and who wants to check a listed figure against its class. It suits less well a household whose hot-water use is much heavier or lighter than the test draw. The registry lists a maximum flow rate in gallons per minute of 3.5. The conditions behind that rating are not available here, so this page cannot say how the unit performs with several fixtures running.

Running cost is not written in this text because it depends on the state average residential gas price, which differs by reader. The cost calculator applies that price to the 122 therms for T-H3M-OS-N 1** once you enter your ZIP. The steps behind that calculation are described in how the annual cost is calculated. The modeled installed-cost range appears in its own block with its source and date, and it is a modeled range, not a quote. To compare this unit with another in the same class, find a same-class replacement by model number and read its energy at the medium draw pattern. A comparison across different draw patterns would not use the same daily draw.