Process Technology's SmartOne PTC electric immersion heaters are self-limiting
Process Technology's SmartOne line of PTC (positive temperature coefficient) electric immersion heaters is cULus listed. SmartOne PTC heaters are designed not to burn out in air.
The PTC heater utilizes solid state ceramic heating elements as its heat source. The devices are “self-limiting” — the maximum temperature is internally limited regardless of the operating conditions. Traditional resistance heaters have the potential for a runaway heat condition if operated out of solution, but the PTC heater can self limit its maximum temperature regardless if operated in water, air or surrounded by buildup.
If the temperature goes down, so does the resistance (thereby increasing power output). If the heat transfer is restricted, the temperature will increase (as will the resistance), resulting in reduced power output.