A heater system includes a heater bundle having a plurality of heater assemblies and a plurality of power conductors. More than one of the heater assemblies includes a plurality of heater units, and more than one of the heater units defines at least one independently controlled heating zone. The plurality of power conductors are electrically connected to the independently controlled heating zones. The heater system further includes means for determining temperature, and a power supply device including a controller configured to modulate power to the independently controlled heating zones through the power conductors based on the determined temperature to provide a desired power output along a length of more than one of the heater assemblies.