With heating screws, which have a heated trough as well as a heated screw shaft, the desired temperature difference can be reached by means of indirect heating. The product flows through the inlet into the spiral screw which carefully transports it to the outlet. The conveyor pipe’s and/or the conveyor trough’s surface is being heated. In order to achieve heating of the conveyor medium, a heat transfer medium circulates inside the double jacket. The desired temperature is reached with the design of the heating surface.