A. O. SMITH TK-510CX3 1**

The 209 therms figure does not appear in the registry itself. This site computed it from two inputs. The first is the model's UEF, the ratio of hot water delivered to energy used, which the registry lists as 0.81. The second is the DOE test's daily hot-water draw for the high draw pattern. The underlying record comes from the DOE CCD, retrieved 2026-09-19. The figure holds only at the federal test's daily draw. A household that draws more or less hot water will use a different amount, and that amount is not available here. The steps behind the calculation are set out in how this site calculates annual energy and cost.

The high draw pattern stands for a larger household, or one where showers and laundry overlap. The comparison group is the 397 models registered as a gas tankless unit at that pattern. Their median is 182 therms a year, and this model uses 27 therms more. That places it in the highest quarter of its class for energy use. Its maximum flow rate in gallons per minute is 5, as listed in the registry. A reader checking flow for a household can take that registry figure as stated. A reader who wants lower gas use at the same test draw should note that most of the class registers less. Models in the same class can be listed through a same-class replacement search by model number.

Running cost is not stated in this text. It depends on the state average residential gas price, so the page computes it from your ZIP. The same 209 therms at the high draw pattern gives a different cost in each state. The 27 therms gap above the class median raises the cost at any given rate, but its size depends on that rate. For a figure on your own rate, use the water heater cost calculator for your ZIP. The installed price appears in its own block, with its source and date. It is a modeled installed-cost range, not a quote, and this text does not restate it.