he ENERGY STAR rated NRC661, Noritz’s newest efficient condensing model with a half inch gas line. Featuring the same energy-saving condensing technology as the rest of the Noritz eco-TOUGH™ Series of gas-fired residential tankless water heaters, the NRC661 has an Energy Factor of 0.91 for natural gas and 0.93 for LP. These ratings are nearly 10 points higher than that of a comparably sized, conventional tankless unit, and approximately 30 points higher than a standard, tank-type gas-fired water heater.
With a maximum input of 120,000 BTU per hour (BTUh), using a half-inch gas line up to 120 feet in length. A new, more accurate interpretation of the National Fuel Gas Code permits the use of the smaller-diameter gas piping for inputs up to 174,000 BTUh, as long as the water column pressure at the inlet of the unit is a minimum eight inches.