A controller system for a biofuel-fired furnace , the system comprising: a fuel feed controller connectable to a motorized fuel feed device of the biofuel furnace and configured to generate first signals for controlling operation of the fuel feed device; a supply air controller connectable to a supply air handler of the biofuel furnace and configured to generate second signals for controlling operation of the supply air handler; a heat demand calculator connected to at least one fluid temperature sensor and a fluid flow rate sensor coupled to the biofuel furnace, so as to repeatedly receive signals from the sensors, wherein the fluid is a heat-transfer medium, the heat demand calculator being configured to repeatedly calculate, based at least in part on the signals from the sensors, an amount of heat being extracted from the heat-transfer medium circulated in and out through the biofuel furnace; and a heat production adjuster coupled to the heat demand calculator, to the fuel feed controller and to the supply air controller, the heat production adjuster being configured to: repeatedly monitor the amount of heat being extracted from the heat-transfer medium; repeatedly recalculate a rate at which the fuel feed device should deliver fuel to the biofuel furnace, based at least in part on a current amount of heat being extracted from the heat-transfer medium; repeatedly recalculate a rate at which the supply air handler should deliver air to the biofuel furnace; and cause the fuel feed controller and the supply air controller to operate the fuel feed device and the supply air handler, respectively, according to the recalculated rates. a fuel feed controller connectable to a motorized fuel feed device of the biofuel furnace and configured to generate first signals for controlling operation of the fuel feed device; a supply air controller connectable to a supply air handler of the biofuel furnace and configured to generate second signals for controlling operation of the supply air handler; a heat demand calculator connected to at least one fluid temperature sensor and a fluid flow rate sensor coupled to the biofuel furnace, so as to repeatedly receive signals from the sensors, wherein the fluid is a heat-transfer medium, the heat demand calculator being configured to repeatedly calculate, based at least in part on the signals from the sensors, an amount of heat being extracted from the heat-transfer medium circulated in and out through the biofuel furnace; and a heat production adjuster coupled to the heat demand calculator, to the fuel feed controller and to the supply air controller, the heat production adjuster being configured to: repeatedly monitor the amount of heat being extracted from the heat-transfer medium; repeatedly recalculate a rate at which the fuel feed device should deliver fuel to the biofuel furnace, based at least in part on a current amount of heat being extracted from the heat-transfer medium; repeatedly recalculate a rate at which the supply air handler should deliver air to the biofuel furnace; and cause the fuel feed controller and the supply air controller to operate the fuel feed device and the supply air handler, respectively, according to the recalculated rates. repeatedly monitor the amount of heat being extracted from the heat-transfer medium; repeatedly recalculate a rate at which the fuel feed device should deliver fuel to the biofuel furnace, based at least in part on a current amount of heat being extracted from the heat-transfer medium; repeatedly recalculate a rate at which the supply air handler should deliver air to the biofuel furnace; and cause the fuel feed controller and the supply air controller to operate the fuel feed device and the supply air handler, respectively, according to the recalculated rates. <EOS>