AMERICAN TK-510CX3 1**

The 209 therms figure is computed by this site, not read from the registry. It combines the registry's UEF, the ratio of hot water delivered to energy used, with the federal test's daily hot-water draw. The listed UEF is 0.81. The source is DOE CCD, retrieved 2026-09-19. The unit's maximum flow rate in gallons per minute is 5. The figure applies only at the high draw pattern and is stated in therms of natural gas. A different daily draw would give a different figure. Method details are on the page explaining how the annual cost is calculated.

Against its class, this unit uses 27 therms more than the class median of 182 therms. Its rank of 323rd lowest of 397 puts it in the highest quarter of its class for energy use. The class holds only models registered as a gas tankless unit at the high draw pattern. That pattern fits a larger household, or one where showers and laundry overlap. For a household with lighter use, the 209 therms figure does not apply, and this page has no figure for other draw patterns. To compare same-class units by model number, you can find a same-class replacement by model number.

Running cost is not stated in this text. It depends on the state average residential gas price for your location. Multiplying 209 therms by that price per therm gives the yearly gas cost at the high draw pattern. The cost calculator on your own ZIP applies that price for you. The modeled installed-cost range appears in its own block on this page, with its source and date. It is a modeled range, not a quote, so it is not restated here. The gap of 27 therms to the class median of 182 therms does not change with your rate; only the cost does.