The NHB (NAVIEN heating boiler) Series from NAVIEN is available in four sizes (NHB-55, NHB-80, NHB-110 and NHB-150) with turndown ratios of 7-to-1, 10-to-1, 11-to-1 and 15-to-1. The 15-1 turndown ratio in the NHB-150 is achieved with the burner system, which includes a dual venturi gas delivery system. The boilers carry the ENERGY STAR 2015 Most Efficient rating and include smart control features for high-efficiency installation. 800/519-8794; us.navien.com.