Abstract The subject of this paper is one which is indeed much broader than could be expected from a casual glance, due to the many types of furnaces used for the various rolling-mill operations. The subject matter is confined to those furnaces used for reheating purposes, necessary for serving, rolling, and piercing mills. Even this reduced field leaves it an extremely broad one when considering the types of furnaces required for the different operations. The author discusses the various classes, using only broad subdivisions of each, and with this in mind a chart is given to show this classification, in order to permit of some common points of comparison, both as to design and operation.