A heater system (10) includes a heater bundle (12) with heater assemblies (18), at least one of the heater assemblies (18) having a plurality of heater units, at least one heater unit having an independently controlled heating zone, and the at least one heater assembly (18) having a physical construction configured to deliver a variable power output per unit length along a length of the at least one heater assembly (18). A plurality of power conductors are electrically connected to the plurality of heater units and the heater system (10) further includes a means for determining temperature. A power supply device (14) includes a controller (15) configured to modulate power to the independently controlled heating zone through the power conductors based on the determined temperature to provide a desired power output along a length of the at least one heater assembly (18).