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early 13c., from Old French fornaise "oven, furnace" (12c.), from Latin fornacem (nominative fornax) "an oven, kiln," related to fornus, furnus "oven," and to formus "warm," from PIE root *ghwer- "warm" (cf. Greek thermos, Old English wearm; see warm (adj.)).
(1.) Chald. attun, a large furnace with a wide open mouth, at the top of which materials were cast in (Dan. 3:22, 23; comp. Jer. 29:22). This furnace would be in constant requisition, for the Babylonians disposed of their dead by cremation, as did also the Accadians who invaded Mesopotamia. (2.) Heb. kibshan, a smelting furnace (Gen. 19:28), also a lime-kiln (Isa. 33:12; Amos 2:1). (3.) Heb. kur, a refining furnace (Prov. 17:3; 27:21; Ezek. 22:18). (4.) Heb. alil, a crucible; only used in Ps. 12:6. (5.) Heb. tannur, oven for baking bread (Gen. 15:17; Isa. 31:9; Neh. 3:11). It was a large pot, narrowing towards the top. When it was heated by a fire made within, the dough was spread over the heated surface, and thus was baked. "A smoking furnace and a burning lamp" (Gen. 15:17), the symbol of the presence of the Almighty, passed between the divided pieces of Abraham's sacrifice in ratification of the covenant God made with him. (See OVEN.) (6.) Gr. kamnos, a furnace, kiln, or oven (Matt. 13:42, 50; Rev. 1:15; 9:2).
structure in which useful heat is produced by combustion or other means. Historically, the furnace grew out of the fireplace and stove, following the availability of coal for heating. A coal furnace is made up of several elements: a chamber containing a grate on which combustion takes place and through which ashes drop for disposal; a chimney to carry away smoke and provide a draft of air; another source of air supply to help burn volatile gases and hydrocarbons; and a metal surface over which the hot gases pass and which transfers heat to circulating water or air. Coal furnaces are still widely used in industry, where they are usually equipped with mechanical stokers.