An assembly suitable for controlling the temperature of a workpiece operatively engaged thereby is provided. The assembly generally comprises a housing characterized by first and second housing members sealingly united at their peripheries, and a heater cartridge enclosed within the housing and compressively retained interior of the sealingly united peripheries of the housing members. The heater cartridge comprises a heat conducting casing characterized by first and second heat conducting casing members and a composite heating element compressively retained between the heat conducting casing members. The first and second heat conducting casing members are selectively united interior of their peripheries so as to delimit heat conduits for the heater cartridge.