AMERICAN TK-510U-I 2**

The figure of 209 therms is not a registry value. This site computed it from the registry's UEF, the ratio of hot water delivered to energy used, which is 0.81 for this model, and the DOE test's daily hot-water draw for the high draw pattern. The registry data came from DOE CCD, retrieved on 2026-09-19. It describes the federal test's draw, not measured use in any particular home. A household that draws more or less hot water than the test assumes will use a different amount. The maximum flow rate in gallons per minute is 5; the site's calculation does not use it.

Among the 397 models registered as a gas tankless unit at the high draw pattern, this one ranks 323rd lowest energy use of 397. That places it in the highest quarter of its class for energy use. The class median is 182 therms, and this model sits 27 therms above it. The high draw pattern describes a larger household, or one where showers and laundry overlap, so the comparison is against units tested under the same conditions. The figure applies to that kind of household and does not describe a smaller one. To check a same-class alternative, use find a same-class replacement by model number.

The running cost is not stated here because it depends on your state's average residential gas price. The cost calculator for your own ZIP applies that price to 209 therms at the high draw pattern. The steps behind the result are described in how the annual cost is calculated. Because this model sits 27 therms above the class median of 182 therms, the same gas price gives a higher annual cost than for a median model at the same draw. Energy use at other draw patterns is not available on this page. The installed price range appears in its own block, with its source and date, as a modeled range and not a quote.