The Premium Non-condensing (NPN) series tankless water heaters will be offered in two series, the NPN-U (universal) and NPN-E (exterior), both of which will be available in 160,000 Btu/h, 180,000 Btu/h and 199,900 Btu/h models for either natural gas or liquid propane. The series features NaviTech technology that includes a stainless-steel heat exchanger and an advanced stainless-steel burner. The NPN-U series are the first and only non-condensing tankless water heaters to offer indoor and outdoor operation within the same unit and include an integrated control panel within the cover of the unit, the company says. Both have recirculation control built into their circuit boards and are designed with a pin-to-pin matching configuration for easy retrofit installations. Navien.