Modern steel is produced using either the blast furnace or arc furnaces. The basement generally contained a large natural convection furnace or boiler. The Sloss Furnaces has an annual Halloween haunted attraction called "Sloss Fright Furnace". The resultant heat was used to preheat the air blown into the furnace. The boiler is a rectangular furnace about on a side and tall. One design was the shaft kiln, similar in design to a blast furnace. The solidified ingots then head for a vacuum induction melting furnace. This was a particular concern in smelting iron using a blast furnace. Both reverberatory furnace and electric furnace can be used. Cool air was returned through similar large ducts leading to the bottom of the furnace. Dampers are used to control the quantity of air admitted to the furnace. The process for these machines start with melting the metal in a separate furnace. Robertson later built an iron plantation in Cumberland Furnace. Nozzles used for feeding hot blast into a blast furnace or forge are called tuyeres. The basement contains storage, a furnace, and the laundry.