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The Navien NPE-180S2 is a condensing tankless water heater with a 10,000–150,000 BTU input range and a 0.96 UEF, among the most efficient gas tankless units sold. It delivers 8.4 GPM at a 35°F rise and 4.3 GPM at a 67°F rise, enough for a whole house in mild climates and one to two bathrooms in cold ones. It ships with a natural gas to propane conversion kit, mounts indoors or outdoors on a wall, and vents with 2-inch PVC up to 75 feet. Against the NPE-240S2 it trades some output for a smaller gas line and vent footprint; against non-condensing rivals it costs more upfront but wastes far less heat.
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Owners and installers of the NPE-180S2 line praise its efficiency, quiet operation and steady temperature, and the included propane kit is a common plus. Complaints center on cold-climate output and installation complexity rather than reliability.
The Navien NPE-180S2-NG is a condensing tankless water heater that heats water on demand instead of storing it in a tank. It has a heat input of up to 150,000 BTU/h and a 0.96 Uniform Energy Factor. Two stainless steel heat exchangers do the heating. The manufacturer designed it for residential or light commercial use.
It mounts on a wall, indoors or outdoors, which frees up floor space. It uses electronic ignition and is engineered to run with minimal noise. It can run on natural gas or propane, and the included conversion kit switches it from natural gas to propane.
It vents with 2" or 3" PVC, CPVC, polypropylene, or stainless steel. Safety features include flame rod detection, an air pressure switch, water and exhaust temperature limit switches, power surge and burner high-limit fuses, and a vent installation detector.
