TAKAGI TK-510U-I 2**

The 209 therms figure is calculated by this site. It does not come directly from the registry. It combines the registry's UEF, the ratio of hot water delivered to energy used, with the daily hot-water draw that the DOE test sets for the high pattern. For this model the UEF is 0.81, so the estimate holds only at that test draw. A home that uses less hot water than the test assumes would use less gas. A home that uses more would use more gas. How far a particular home differs from the test is not available in this data. The source is DOE CCD, retrieved 2026-09-19. The steps behind the estimate are set out in how the annual cost is calculated.

The high draw pattern describes a larger household, or one where showers and laundry overlap. The registry lists this unit's maximum flow rate in gallons per minute as 5. Among the 397 gas tankless units registered at this draw pattern, its energy use puts it in the highest quarter of the class. Other models in the same class use less gas at the same test draw, so the 27 therms gap to the median is measured against that test. Whether the gap holds for a particular home cannot be known here, because the data does not include that home's actual hot-water use. To list other registered units in the same class, use the same-class replacement search by model number.

The text on this page does not give a running cost. The cost of using 209 therms a year at the high draw pattern depends on the reader's state average residential gas price. The page looks up that price from the reader's ZIP. No cost figure is written here, and none is estimated. The 27 therms gap to the class median is a gap in gas use. What that gap costs changes with each state's rate. The installed price range appears in its own block, with its source and date. It is a modeled range, not a quote. To work out the running cost for a given location, use the running-cost calculator for your own ZIP.