Navien expands its premium condensing tankless NPE water heater series with the addition of the NPE-150S model. This smaller size “S,” Standard version with an efficiency of 0.97 EF has a heating capacity of 18,000-120,000 btu/hr., and will produce 5.3 gpm at 45° temperature rise. This water heater is ideal for small residences or to cascade where a bit more DHW is required.