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If the heater cable is self-regulating, do I need a controller?
That depends on how precisely you need to control the temperature of the pipe. If tight control is required, a line sensing device is best. For freeze protection applications, an ambient sensing controller often used with self-regulating heating cables. When using a line sensing controller, a separate controller should be used for each unique flow condition.
How should I decide whether to use ambient or pipe sensing controllers?
Ambient sensing controllers typically offer a simpler installation and lower material cost, since one thermostat can control multiple pipe segments. However, energy costs will be higher, since the controller does not respond to changes in pipe temperature. (Think of the heat in your house -- if the thermostat was on the front porch instead of in your living room, the heat would be on most of the winter, keeping the house much warmer than needed and energy bills higher than necessary.)
Pipe sensing controllers are more precise and energy efficient, but can have a higher initial material and installation cost since a separate controller is required for each unique pipe size and flow condition. Controlling multiple pipes with a single pipe sensing controller can lead to freeze ups.
For a single pipe run, pipe sensing controllers are usually the best option. For mutliple pipes, consider the balance between upfront cost and long term operating costs. For long pipe runs or where total electrical loads are high, the initial cost differential for pipe sensing controls can be an economical choice in the long run.
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