A. O. SMITH T-H3S-OS-N 1**

The registry lists a UEF, the ratio of hot water delivered to energy used, of 0.94 for A. O. SMITH T-H3S-OS-N 1**. The annual figure is computed by this site, not the registry. It combines that UEF with the DOE test's daily hot-water draw for the high draw pattern, using DOE CCD data retrieved 2026-09-19. The result is 180 therms. Against the 397 models registered as a gas tankless unit at the high draw pattern, the class median is 182 therms, so this model sits 2 therms below it. It ranks 165th lowest energy use of 397, which is the second-lowest quarter of its class. The steps of the calculation are set out on the methodology page for water heater cost.

The high draw pattern describes a larger household, or one where showers and laundry overlap. The figure of 180 therms belongs to that pattern only. Energy use at any other draw pattern is not available on this page, so the figure should not be read as a value for a smaller household. The registry also lists a maximum flow rate in gallons per minute of 5.3. The data here does not say how many fixtures that rate serves at once, and it does not show how the unit performs in a particular home. To compare units by fuel, space and size, use the water heater selector.

Running cost is not stated in the text because it depends on the state average residential gas price, which differs from one reader to the next. The page computes it from your ZIP, and the cost calculator applies that price to the 180 therms of natural gas. The installed price range appears in its own block, as a modeled installed-cost range and not a quote, so it is not repeated here. Whether the 2 therms gap to the class median of 182 therms changes a yearly bill cannot be stated without your rate. To find a unit in the same class, look up a same-class replacement by model number, starting from T-H3S-OS-N 1**.