www.phcppros.com/articles/7891-navien-npe-tankless-water-heaters

Navien NPE Tankless Water Heaters
July 25, 2018
NPE series condensing tankless water heaters, for both commercial and residential applications, feature: ComfortFlow recirculation including pump and buffer tank, ½-inch gas pipe capability, 2-inch PVC venting, dual stainless steel heat exchangers, field gas convertibility and a compact design. Up to 16 units can be cascaded together and eight units may be common vented. The NPE-180A, NPE-210A and NPE-240A are also available with HotButton on demand activation and NaviLink wi-fi control.
For installations where the internal pump and buffer tank are not required, the NPE-S series is recommended. It is available in four sizes, NPE-150S, NPE-180S, NPE210S and NPE-240S.
Navien