Noritz NR501-OD-LP

The annual figure of 135 therms is calculated by this site, not by the registry. The calculation starts from the registry's UEF, the ratio of hot water delivered to energy used. It then applies the daily hot-water draw that DOE assigns to the medium pattern. The registry lists a UEF of 0.82 for this unit. The result applies to natural gas only, and only at the medium draw pattern. The source is the DOE CCD, retrieved on 2026-09-19. A household that draws more or less hot water than the test assumes will use a different amount of gas.

Among the 80 models registered as a gas tankless unit at the medium draw pattern, the median is 135 therms. This unit uses 135 therms, so its difference from the median is 0 therms. It ranks 32nd lowest, which places it in the second-lowest quarter of its class for energy use. The registry lists a maximum flow rate in gallons per minute of 3.1. That value describes flow capacity and is not part of the energy calculation. The data here does not rank the unit on anything other than energy use at this draw pattern.

This figure suits a reader whose household uses hot water like the medium pattern, a typical household on a busy morning. It is less useful for a household with much heavier or lighter use, because 135 therms was not calculated for that draw. Running cost is not stated here, since it depends on your state's average residential gas price. Enter your ZIP in the cost calculator to apply your own rate to 135 therms. The method for the annual cost is documented separately. To compare units in the same class, find a same-class replacement by model number. The modeled installed-cost range is shown in its own block and is not a quote.