Navien NFB series high-efficiency condensing fire tube boilers are available in two models, NFB-175 (175,000 Btu/h) and NFB-200 (199,900 Btu/h). Each model features a new in-house designed and manufactured, patented heat exchanger that is robotic laser welded and form-pressed to minimize the number of weak points that could be prone to thermal stress and corrosion. The Energy Star Most Efficient 95% AFUE NFB series includes advanced controls with intuitive display, cascade capability up to 16 units, common venting capability up to 8 units, 10:1 turndown ratio and field gas convertibility.