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.

A fire placed at the foot of the upcast shaft, the gas laden air from the mine would rise with the heat and create a circulatory ventilation process. Replaced in later years with powerful fans

a stone stack shaped like a pyramid with the top part taken off, where iron ore was smelted into iron

Place for melting glass, built of several kinds of high temperature (refractory) materials to hold the glass and hold in the heat without breaking down during the several months that furnaces usually run. See also Tank, Pot Furnace, and Refractory.