An inclosed place in which heat is produced by the combustion of fuel, as for reducing ores or melting metals, for warming a house, for baking pottery, etc.; as, an iron furnace; a hot-air furnace; a glass furnace; a boiler furnace, etc. Note: Furnaces are classified as wind or air. furnaces when the fire is urged only by the natural draught; as blast furnaces, when the fire is urged by the injection artificially of a forcible current of air; and as reverberatory furnaces, when the flame, in passing to the chimney, is thrown down by a low arched roof upon the materials operated upon.