In the past, the center of iron production was not in the Ruhrgebiet, but in the Sauerland and Siegerland regions. This was due to the abundance of forests and ore in these areas, since, in addition to the ore itself, large quantities of charcoal were required for smelting iron at that time. In addition, due to the infertile soil and unfavorable weather conditions in this mountainous part of the country, the population had to look for sources of income other than agriculture even back then.
The name “Rennfeuer” is derived from the German verb “zerronnen” or “to let run off,” referring to the slag. In 1965, Manfred Sönnecken discovered the best-preserved Rennofen in the Märkisches Sauerland in the immediate vicinity of Gut Berentrop; it was dated to the 13th century. The furnace is made of clay and loam and has a hearth diameter of 50 cm and a shaft height of 80 cm, though it likely originally stood about 130–150 cm tall. The furnace outlet, which had been sealed during the smelting process, was broken open by the ironworkers after smelting to allow the molten slag to drain out and to pull out the “Eisenluppe”—that is, the lump of iron.
To prevent the now-open cupola furnace from further disintegration, this section had to be restored. In the left wall of the furnace, 20 cm above the floor, there is a fist-sized air hole that originally held a fired clay nozzle (inner diameter 3 cm). Air was blown into the furnace interior here using a foot-operated bellows mounted in a trough-shaped recess. The iron ore was mined in the adjacent open-pit mine and transported to the smelting site. Here, the ore was processed by crushing it to the size of nuts and peas and roasting it in a charcoal fire.
The charcoal, which also served as fuel for the furnace, was produced at surrounding charcoal kilns. A single smelting process consumed about 150 kg of ore and 500 kg of charcoal, yielding, after approximately 8to 9 hours, a lump of raw iron weighing about 15 kg—which was still significantly contaminated by charcoal and slag—was produced and subsequently processed further in the forges.
With the support of the town of Neuenrade, the Märkischer Kreis, and the Westphalian Office for the Preservation of Historical Monuments, a protective shelter was built for the cupola furnace in 1983, making this technical cultural monument accessible to all interested citizens.
Tour The blast furnace can be toured at any time or by appointment with Mr. Peter Heymann (02392/507240).