Abstract: An extruder system includes a barrel surrounded by a jacket defining a plurality of zones. Other zones may be in the feed screw and downstream processes. A temperature control unit has a hot water circuit and a cold water circuit each with supply and return manifolds and valves which allow connection of each of the zones to receive either hot or cold water. Each circuit has a single heat exchanger which is used to heat or cool all the water circulating in the respective circuit. The two circuits may be interconnected by a heat pump so that waste heat from the cooling circuit is used by the heating circuit. In this case the heat exchangers become auxiliary. The system permits optimum energy reuse from heated areas to cooled areas, or vice versa, and minimizes additional energy requirements.