Establish a maximum temperature at which the part will operate.
Determine total wattage needed to produce this temperature.
Establish the largest diameter and the length of the cartridge heater that is best suited to the dimensions of your part.
Estimate the number of heaters needed for even heat. Divide the total wattage by the number of cartridge heaters to determine the wattage rating of each heater.
Determine the watt density of the size selected (3.14 * diameter * length = area. Wattage / Area = watt density).
Determine fit (subtract minimum outside diameter of the heater from maximum inside diameter of hole).
If you find that the watt density is excessive, you can correct it in one of three ways:
Use a tighter fit.
Use more or larger heaters.
Use a lower wattage and allow for a longer start up time.
