Thermal energy storage to increase furnace efficiency

A forced air heating system including:

• a furnace comprising a combustion chamber for burning a flowable fuel as a source of heat, means for controlling the flow of fuel to said combustion chamber, inlet duct means and discharge means for the circulated air flowing through said furnace, and a primary heat exchanger associated with said combustion chamber for heating the circulated air;
• a stack for discharging flue gases from said primary heat exchanger;
• and a blower for effecting the flow of circulated air through said furnace and the space to be heated;
• wherein the improvement comprises:
• a recuperator exchanger comprising a body of a phase change material, disposed in heat exchange relation with the flue gases flowing through said stack, and flow path means for conveying the circulated air in heat exchange relation with said body;
• duct means connecting said recuperator exchanger between said inlet duct means and said discharge duct means;
• bypass duct means connected between said inlet duct means and said discharge duct means, for bypassing said recuperator exchanger;
• gate means for effecting the flow of circulated air alternatively through said recuperator exchanger and said bypass duct means;
• and actuator means, responsive to the temperature of said phase change material, for controlling said fuel flow control means and said gate means.