Noritz NR662-OD-NG

The registry lists a UEF, the ratio of hot water delivered to energy used, of 0.82 for this unit. This site computed 135 therms per year from that UEF and the DOE test's daily hot-water draw for the medium draw pattern. The registry itself does not publish that annual figure. The inputs come from DOE CCD, retrieved 2026-09-19. Among the 80 models registered as a gas tankless unit at the medium draw pattern, it has the 32nd lowest energy use. That places it in the second-lowest quarter of its class. Its energy use equals the class median of 135 therms, a difference of 0 therms.

It suits a household whose hot-water use resembles the medium draw pattern, a typical household on a busy morning. For that use, 135 therms of natural gas per year is the value to compare against. The unit's maximum flow rate in gallons per minute is 3.6. The data here does not state the temperature rise behind that flow rate. It suits less well a household with much higher or lower daily use. Its gas use would differ, and this page gives no estimate for other draw patterns. The water heater selector filters by fuel, space and size.

The running cost is not stated in this text. It depends on the state average residential gas price, which varies by location. Multiply 135 therms by your own gas price per therm to get a yearly cost at the medium draw pattern. The cost calculator works this out from your ZIP. The methodology page explains how the annual cost is calculated. The replacement finder lists a same-class model when you enter a model number. The modeled installed-cost range appears in its own block, with its source and date, and is not repeated here.