AMERICAN TK-510C-NI 1**

The 209 therms figure comes from this site's own calculation, not from the registry. The calculation starts with the registry's UEF, the ratio of hot water delivered to energy used. It then applies the daily hot-water draw that the DOE test sets for the high draw pattern. This model's UEF is 0.81. The registry values come from the DOE Compliance Certification Database (CCD), retrieved 2026-09-19. Because the figure assumes the test's daily draw, it describes a standard household, not a specific home. Actual gas use depends on how much hot water a household really draws, and this figure does not measure that. The method behind the annual energy and cost figures sets out each step of the calculation.

The high draw pattern stands for a larger household, or one where showers and laundry overlap. The registry lists this unit's maximum flow rate in gallons per minute as 4.7. The other 397 models registered as gas tankless units at this pattern make up its class. It ranks 323rd for lowest energy use among them, which puts it in the highest quarter of its class for energy use. A reader looking for lower annual gas use at this draw pattern will therefore find most same-class models below it. A reader who needs a unit in the same class can find a same-class replacement by model number. The registry data used here does not cover noise, venting or service history, so this page does not assess them.

This text does not state the running cost. The cost depends on your state's average residential gas price, so the page computes it from your ZIP. The same 209 therms gives a different cost in each state. Likewise, the 27 therms gap above the class median only becomes a cost gap once a gas rate is applied. The installed-cost range shown in its own block on this page is a modeled range with its own source and date. It is not a quote. To see the yearly cost of this model at your gas rate, open the running-cost calculator for your ZIP.