What is the desired temperature of the item to be heated? What is its starting temperature? A higher output heater is needed to boil a pot of water sitting outside in the cold as compared to the same pot of water inside a warm kitchen.
Heating Speed / Ramp-up Time
How quickly does the part need to reach the desired temperature?
Materials to be Heated
What materials are used to build the item to be heated?
A thin copper pipe will transfer heat very differently than a thick plastic one.
Heated Area Size and Dimensions
Consider the shape and area available to attach a heater, as well as the space available to perform the physical installation.
What are the electrical requirements of your situation? Do you have 120V or 240V power available? Information such as voltage, amperage, or wattage desired is essential to designing the correct heater for your application.
Temperature Control Elements Desired
Do you require any temperature control elements to help you monitor and control the heat output of the heater? If so, what are the requirements for the temperature control system you are using?
Wire Exit Locations
Where should the lead wires exit the heater? From the top, side, or bottom? What is the most convenient for your installation?
Can the heater be permanently attached with an adhesive or does it need to be removable?