 Iron plantations in Alabama, Tennessee, Georgia, Michigan, Wisconsin, and Missouri in particular better survived the evolving technological landscape by adopting practices that increased charcoal energy efficiency, that is, the amount of charcoal consumed per ton of iron smelted.One such technique was to raise the heights of furnaces to create a longer and more uniform reaction chamber to produce more homogeneous pig iron.Whereas antebellum furnaces were built with brick and mortar and reached only 30-35 feet in height, new furnaces remodeled in the 1840s reached as high as 65 feet.