Joanna Furnace used a Blowing Engine House and hot blast area to modernize ironmaking in 1888, when a Weimer model 1889 steam engine helped power the furnace by replacing the giant waterwheel that had driven blast machinery. In this system, hot gases from the stack were sent through a downcomer pipe to a boiler behind the engine house, producing steam for the engine and heat for the hot blast. Invented in 1829, the hot blast method superheated blast air before it entered the furnace, retained more heat than the cold blast method, reduced the amount of charcoal needed, and doubled iron production. During its short hot blast period from 1888 to 1898, Joanna Furnace continued to use charcoal rather than coal or coke throughout its 107 years of operation. The furnace stack, built in 1791 of native sandstone to a height of 28 feet and later raised to 45 feet, was set into a hillside so iron ore, limestone, and charcoal could be dumped into the top. Inside, the firebrick bosh formed the smelting chamber, with hearth, lower bosh, and upper bosh sections, and molten iron was tapped from the hearth. Ironmaking began by filling the bosh with charcoal and lighting it from the top, then refilling it, applying a cold air blast through tuyeres, and adding increasing charges of charcoal, iron ore, and limestone. Powered first by water-driven bellows, the process took several days before slag and molten iron flowed into the hearth, and the furnace was charged every half hour while molten iron was tapped every twelve hours. In the Casting House, a stone building beside the stack, castellated openings vented heat and admitted cooler air, while a beaver-tail tile roof protected the structure from heat and sparks. Furnace operation required founders, keepers, guttermen, fillers, moulders, and other laborers working day and night in twelve hour shifts for nine to thirteen months while the furnace was in blast. These skilled workers were English, Welsh, Irish, German, and African Americans. Usually twice a day, molten iron was tapped from the bosh and run or ladled into blackened sand molds in the Casting House to make pig iron, floor castings, and flask castings. In 1840, Joanna Furnace produced 2,200 tons of pig iron and 500 tons of castings, and among the items made there were in-plate stoves, sash weights, bake ovens, pots, pans, kettles, fire backs, and cannon ball.
