Viessmann Vitodens 100-W B1HE-199 vs Navien NFB-200H

Both boilers are heating-only condensing units rated 95% AFUE on natural gas or propane and both top out in the 199 MBH range — Navien at 199.9 MBH and Viessmann at 199 MBH input (58.3 kW). The minimum fires diverge clearly: the NFB-200H drops to 13.3 MBH while the B1HE-199 stops at 19.9 MBH, so in mild weather and at low part load the Navien can hold a lower firing rate before cycling.

Cabinets and weights move in opposite directions from capacity: the NFB-200H is 17.3 inches wide, 27.6 inches high and 17.3 inches deep at 121 lb (148 lb with water), while the B1HE-199 measures 17.75 by 39 by 21.75 inches and weighs 179 lb (81 kg). For a retrofit in a low, tight mechanical room, that 11-inch height difference is often the deciding factor on its own.

Both makers list similar venting flexibility in their own terms — Navien allows 2" to 65 feet or 3" to 150 feet per side, and Viessmann quotes about 180 ft of venting for the B1HE series with per-size limits in its technical data manual. Both are heating-only, so domestic hot water comes from an indirect tank, and both are sized from a heat-loss calculation rather than the model number.