Abstract: A forced air furnace circulation fan controller adjusts the speed of the circulation fan according to the incidence of air delivery restrictions. Upon detecting insufficient air delivery as a function of the temperature of the furnace heat exchanger, the control system increases the circulation fan speed to increase the air delivery within the heating system. The controller utilizes fuzzy logic techniques to determine a speed adjustment for the furnace fan motor, based on the value of the furnace heat exchanger temperature. The use of fuzzy logic control allows the circulation fan controller to provide a highly adaptive response to changes in air delivery. The resulting balanced air delivery provides for efficient furnace operation and superior occupant comfort.