Oven heating system

Claim 1

IN AN AIR CIRCULATING SYSTEM FOR AN OVEN PROVIDED WITH AN ENDLESS TRAVELING TRAY CONVEYOR FOR TRANSPORTING PRODUCTS TO BE BAKED THERETHROUGH IN AN UPPER AND A LOWER LONGITUDINALLY EXTENDING RUN, AN IMPERFORATE HORIZONTAL PARTITION BETWEEN SAID UPPER AND LOWER TRAY CONVEYOR RUNS EXTENDING FROM ONE SIDE OF THE OTHER OF THE OVEN TO PROVIDE THEREIN AN UPPER AND A LOWER BAKING CHAMBER, PERFORATE HORIZONTAL PARTITIONS ABOVE AND BELOW SAID UPPER TRAY CONVEYOR RUN PROVIDING IN SAID UPPER BAKING CHAMBER AN UPPER AND A LOWER PLENUM CHAMBER, PERFORATE HORIZONTAL PARTITIONS ABOVE AND BELOW SAID LOWER TRAY CONVEYOR RUN PROVIDING IN SAID LOWER BAKING CHAMBER AN UPPER AND A LOWER PLENUM CHAMBER, A BLOWER, FIRST BLOWING DUCT MEANS COMMUNICATING WITH THE DISCHARGE SIDE OF SAID BLOWER AND THE LOWER PLENUM CHAMBER OF SAID UPPER BAKING CHAMBER, MEANS PROVIDING COMMUNICATION BETWEEN THE INTAKE SIDE OF SAID BLOWER AND THE UPPER PLENUM CHAMBER OF SAID UPPER BAKING CHAMBER, SECOND BLOWING DUCT MEANS COMMUNICATING WITH THE DISCHARGE SIDE OF SAID BLOWER, INTAKE DUCT MEANS COMMUNICATING WITH THE INTAKE SIDE OF SAID BLOWER, AND DAMPER CONTROLLED CONNECTING DUCT MEANS SELECTIVELY PROVIDING COMMUNICATION BETWEEN EITHER OF SAID SECOND BLOWING OR INTAKE DUCT MEANS WITH ONE OR THE OTHER OF SAID UPPER OR LOWER PLENUM CHAMBERS OF SAID LOWER BAKING CHAMBER.