Abstract: A furnace for heat treating components, especially relatively long components such as main shafts of gas turbine engines, comprises means for mounting a number of components vertically and conveying them repeatedly around a circular path surrounding one or more heating elements, while simultaneously rotating the components about their vertical axes. This allows uniform heat treatment of the components, even when long treatment times are needed. Loading and unloading chambers adjacent to the main chamber permit automated loading and unloading of components without disturbing the environment within the main chamber.