The Energy Star-rated NRC661 gas-fired tankless water heater from Noritz has an Energy Factor of 0.91 for natural gas and 0.93 for LP, 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. It delivers 6.6 gallons per minute, with a maximum input of 120,000 BTU per hour (BTUh). It can be installed with a 1/2-inch gas connection, eliminating the need to up-size to a 3/4-inch run in replacement situations, the company says.