Abstract: A hydrocarbon heating system comprises a surface control panel and a subsurface heating system, connected by an external power cable which also serves as the data communication link between the two parts. The subsurface heating system includes a heating element and two separate, thermally isolated temperature sensors. One thermal sensor, mounted near the heating element, monitors the temperature of the heating element. Another thermal sensor monitors the ambient temperature of fluid in the borehole. The temperature of the heating element may be varied to maintain an optimal well temperature for the production of hydrocarbons. Downhole electronics convert the thermal sensor outputs to digital data, and modulate the digital data onto a power cable that carries power from the surface to the heating element. A control system at the surface controls the heating element via nested control loops monitoring the temperatures of the borehole fluid and the heating element.