Tankless water heater incorporates a built-in buffer tank 

Navien’s NPE-A series ComfortFlow incorporates a built-in buffer tank and recirculation pump inside the unit, the company says. Navien says the NPE-A series’ return line saves thousands of gallons of water per year. Navien also released the NPE-S series condensing tankless water heaters, which the company says supply maximum inputs from 150,000 to 199,900 Btu per hour and outputs from 148,500 to 197,900 Btu per hour. Navien adds that both the NPE-A and NPE-S series include stainless steel heat exchangers, ½-inch gas lines up to 24 feet and 2-inch PVC venting up to 60 feet.