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Claim 1

IN COMBINATION WITH A CONVENTIONAL HOT AIR HEATING SYSTEM OF THE TYPE INCLUDING A FURNACE HAVING SEPARATE HEATER AND BLOWER UNITS PROVIDED WITH SEPARATE ELECTRICAL CONTROL CIRCUITS CONTROLLED BY SPACE AND PLENUM THERMOSTATS RESPECTIVELY DISPOSED IN SAID CIRCUITS, A PLENUM CHAMBER AND AN EXHAUST PIPE, SUPPLEMENTAL CONTROL MEANS INCLUDING A SUPPLEMENTAL CONTROL CIRCUIT CONNECTED TO SAID HEATER CONTROL CIRCUIT, SUPPLEMENTAL SPACE THERMOSTAT MEANS CONNECTED IN SERIES TO SAID SUPPLEMENTAL CONTROL CIRCUIT FOR CYCLING SAID HEATER UNIT DURING OPERATION OF SAID FURNACE, SAID CONVENTIONAL SPACE THERMOSTAT BEING SET TO ACTUATE SAID HEATER CONTROL AT A GIVEN TEMPERATURE AND SAID SUPPLEMENTAL SPACE THERMOSTAT SERVICING GENERALLY THE SAME AREA AS SAID CONVENTIONAL SPACE THERMOSTAT AND BEING SET TO ACTUATE SAID HEATER CONTROL AT A TEMPERATURE SLIGHTLY ABOVE THE SETTING OF SAID CONVENTIONAL SPACE THERMOSTAT, SAID SUPPLEMENTAL CONTROL INCLUDING AN OUTWARDLY AND DOWNWARDLY INCLINED PASSAGE COMMUNICATING THE INTERIOR OF SAID PLENUM WITH THE EXTERIOR OF SAID FURNACE, A THERMOSTAT CONNECTED IN SERIES IN SAID SUPPLEMENTAL CONTROL CIRCUIT, DISPOSED IN SAID PASSAGE TO OPEN SAID SUPPLEMENTAL CONTROL CIRCUIT IN RESPONSE TO WARM AIR PASSING DOWNWARDLY AND OUTWARDLY THROUGH SAID PASSAGE.