TAKAGI TK-510C-NI 1**

The 209 therms figure is computed by this site, not taken from the registry. It uses the model's UEF, the ratio of hot water delivered to energy used, which is 0.81. The second input is the daily hot-water draw that the DOE test sets for the high draw pattern. Both come from the DOE Compliance Certification Database, retrieved 2026-09-19. The figure therefore describes gas use at that test draw, not at your household's own draw. The registry does not record how much hot water a given home uses, so actual yearly use for your home is not available here. The steps behind the number are set out in how the annual cost is calculated.

This model is compared with the 397 models registered as a gas tankless unit at the high draw pattern, and it ranks 323rd lowest energy use. Its 209 therms sits 27 therms above the class median of 182 therms. That places it in the highest quarter of its class for energy use. The high draw pattern corresponds to a larger household, or one where showers and laundry overlap. The registry lists its maximum flow rate in gallons per minute as 4.7. If the aim is lower gas use within this same class, the ranking shows that most registered models test lower. You can look one up with the same-class replacement search by model number.

The running cost is not stated in this text. It depends on your state's average residential natural gas price, so the page computes it from your ZIP. That rate is applied to the 209 therms test-draw figure. Because this model sits 27 therms above its class median, that gap in gas use also appears in the cost at whatever rate applies to you. You can rerun the figure on your own rate with the cost calculator for your ZIP. The installed price range appears in its own block on this page, with its source and date. It is a modeled installed-cost range, not a quote.