RELIANCE WATER HEATERS TK-310CX3 1**

The figure of 209 therms per year is not a registry field. This site computed it from the registry's UEF, the ratio of hot water delivered to energy used. The second input is the DOE test's daily hot-water draw for the high draw pattern. For this model the UEF is 0.81. The registry values come from DOE CCD, retrieved 2026-09-19. The figure covers natural gas only. It holds at the federal test's daily draw, not at any one household's actual use. The inputs and steps behind the calculation 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. The TK-310CX3 1** is rated for that use, with a maximum flow rate in gallons per minute of 4.7. Its class is the 397 models registered as a gas tankless unit at the high draw pattern. Within that class, the gap to the median noted above puts its rank at 323rd lowest in energy use. That rank places it in the highest quarter of its class for energy use. A reader who wants a lower-use model of the same class can search with a same-class replacement lookup by model number. Whether the gap matters for a given home depends on that home's actual draw, which the data does not cover.

The running cost is not written in this text, because it depends on your state's average residential natural gas price. The page computes it from your ZIP instead. The gas side of that sum is fixed at 209 therms a year, at the high draw pattern's test draw and a UEF of 0.81. The cost calculator on your own ZIP applies your rate to that figure. A household with lighter daily use than the high draw pattern falls outside this rating. The data holds no energy figure for this model at that lower use, so it is not available here. The modeled installed-cost range appears in its own block on this page, with its source and date.