Navien introduces the NHB (Navien Heating Boiler) series in four sizes for residential and light commercial use: NHB-55, NHB-80, NHB-110 and NHB-150 with turndown ratios respectively of 7:1, 10:1, 11:1 and 15:1. The noteworthy 15:1 TDR in the NHB-150 is achieved with Navien’s dual Venturi gas delivery system. The company will begin selling the new line of boilers in the U.S. and Canada in the fourth quarter. Navien.