STATE TK-510U-I 2**

This site calculates the 209 therms figure; the registry does not publish it. It combines the registry's UEF, the ratio of hot water delivered to energy used, with the DOE test's daily hot-water draw for the high draw pattern. For this model the UEF is 0.81, taken from the DOE CCD and retrieved 2026-09-19. The result holds only at that test draw. A home that uses more hot water than the test assumes will burn more gas, and one that uses less will burn less. This page does not know how much hot water your household actually uses. The steps behind the figure are set out in how the annual cost is calculated.

The high draw pattern stands for a larger household, or one where showers and laundry overlap. This model's maximum flow rate in gallons per minute is 5. That rate is the limit to compare with the fixtures that may run at the same time. Among the 397 gas tankless models tested at the high draw pattern, it ranks 323rd for lowest energy use. That puts it in the highest quarter of its class for energy use. Most models in the class therefore use less gas at the same test draw. Figures for this model at other draw patterns are not available here. If you want the same class with a lower figure, you can find a same-class replacement by model number.

The text does not give a running cost. The cost of 209 therms a year depends on the average residential gas price in your state, so the page calculates it from your ZIP. You can enter it in the water heater cost calculator for your own ZIP. The 27 therms gap to the class median carries over to cost at any rate: that amount of gas times your price is what this model adds each year over the median at the test draw. The installed price is shown in its own block, with its source and date. It is a modeled installed-cost range, not a quote.