An apparatus and method for controlling continuously and discretely the speed of a heat pump compressor as a function of load conditions to run at least up to 150% of its rate-speed when operated in the heating mode to provide initial supplemental heating prior to turning on of electric heaters. The speed of the indoor condenser fan is maintained at its full rated-speed. The operation of the apparatus is controlled by a microprocessor with a program to provide improved performance and minimize energy consumption.