A. O. SMITH T-H3J-OS-N 1**

UEF, the ratio of hot water delivered to energy used, is 0.95 for this A. O. SMITH model. The annual figure of 178 therms of natural gas is not a registry value. This site computed it from the registry's UEF and the DOE test's daily hot-water draw for the high draw pattern, using DOE CCD data retrieved 2026-09-19. The class for comparison is the 397 models registered as a gas tankless unit at the high draw pattern. In that class the median is 182 therms a year, and this model sits 4 therms below it. Its rank is 45th lowest energy use of 397, which places it in the lowest quarter of the class. The method behind the annual calculation is documented separately.

The high draw pattern describes a larger household, or one where showers and laundry overlap. The 178 therms figure applies to that pattern only. This page has no energy figure for other draw patterns, so a household that fits a different pattern cannot read this value as its own. The figure is also for natural gas only, so a home without a gas supply is outside it. The maximum flow rate in gallons per minute is 4.7 for model T-H3J-OS-N 1**. That is the registry's rating for the unit, and it does not show how many fixtures your home runs at once. To compare other fuels and sizes, use the water heater selector.

Running cost depends on the state average residential gas price, so it is not stated in this text. Multiplying 178 therms by a gas price per therm gives a yearly cost at the high draw pattern, and the cost calculator for your ZIP does that with your state's price. Because this model is 4 therms below the class median of 182 therms, its running cost gap against a median unit is that difference multiplied by the same price. The gap does not include installation, and the modeled installed-cost range appears in its own block on this page. If you need another unit of the same class, you can find a same-class replacement by model number.