Available in two models, the NFB series of high-efficiency condensing fire-tube boilers from Navien each features a new, patented fire-tube heat exchanger that is form-pressed and robotically laser welded in-house to reduce weak points prone to thermal stress and corrosion. Oval tubes in the heat exchanger contain internal turbulators to improve the heat transfer rate and structural integrity. The boilers achieve a 95 percent AFUE rating.
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