Navien’s NHB (Navien Heating Boiler), for residential and light commercial use, is available in four sizes: NHB-55, NHB-80, NHB 110 and NHB-150, with turn-down-ratios of 7:1, 10:1, 11:1, and 15:1, respectively. The 15:1 TDR is achieved with a dual-Venturi gas delivery system. With Energy Star’s 2016 Most Efficient rating, it includes smart control features that offer an opportunity to achieve a true high-efficiency installation.