Noritz NRC663-FSV-NG

The figure of 127 therms of natural gas is computed by this site, not published by the registry. It combines the registry's UEF, the ratio of hot water delivered to energy used, of 0.87 with the daily hot-water draw that the DOE test assigns to the medium draw pattern. That pattern stands for a typical household on a busy morning. The figure holds only under that condition, and a household with different usage would have a different figure, which this page does not estimate. The source is DOE CCD, retrieved 2026-09-19. The registry also lists a maximum flow rate in gallons per minute of 3.4. That value describes capacity and is not part of the energy calculation.

Against its class, this model has the 21st lowest energy use among the 80 models registered as a gas tankless unit at the medium draw pattern. Its 127 therms sits 8 therms below the class median of 135 therms, which places it in the second-lowest quarter of the class. That comparison suits a household whose usage matches the medium draw pattern, or a reader checking a listing against the registry. It does not cover a household with much higher or lower usage, and the data here does not rank models by flow rate. To look for a same-class alternative, use find a same-class replacement by model number. To narrow options by fuel, space and size, use the water heater selector.

The running cost is not stated in the text because it depends on your state's average residential gas price. The cost calculator applies that price, from your ZIP, to the 127 therms figure for the NRC663-FSV-NG. The steps behind it are set out in how the annual cost is calculated. The modeled installed-cost range appears in its own block with its source and date. It is a range and not a quote, so it is not repeated here. Measured gas use in your own home is not available in this data. The 127 therms is a test-based figure for the medium draw pattern and should not be read as a meter reading.