Abstract: A microcomputer control system for a furnace is disclosed which provides accurate control of the temperature of the furnace such that the temperature can be quickly increased to a predetermined desired temperature without overshooting the desired temperature. The control system determines the tuning constants of the furnace as a function of the system's response to a predetermined input and, thereafter, uses the determined tuning constants to accurately control the temperature of the furnace. The control system employs a novel method for increasing the temperature of a furnace wherein full power is applied to the furnace heat source until the microcomputer makes the determination, based upon the furnace tuning constants, that power supplied to the furnace must be reduced to prevent the temperature of the furnace from overshooting the desired temperature.