A survey which shows that the working functions of a metallurgical production furnace have to be considered when making a reconstruction and interpretation from written documents, and from furnace remains of iron production in the past. The date and place of origin of the modern blast furnace, i.e. a furnace producing entirely liquid pig iron which could be tapped at intervals, is an unsolved historical problem. Possible places of origin include Germany and Sweden, and dates vary from the 12th to the 16th century. Some confusion is due to the presence during the same period of the high bloomery furnace (Ger. <i>Stückofen</i>), a tall furnace capable of smelting coarse rock ore, but which had to be shut down before the iron could be removed. Recently, some interesting Swedish attempts have been made to use ancient furnace remains, microstructural examination of slag and iron, and calculations based on chemical analysis of slags to establish the type of furnace being employed at Harhyttan, Vinarhyttan, and Lapphyttan. The conclusions reached are contradictory. The authors attempt to resolve the problem by defining clear criteria as to the necessary requirements and design features of the two types of furnace.