Range ventilating hood

Claim 1

IN A VENTILATOR FOR A COOKING APPLIANCE HAVING SURFACE HEATER UNITS OF THE TYPE ADAPTED TO BE POSITIONED ADJACENT A WALL OF A BUILDING, SAID VENTILATOR OF THE TYPE HAVING WALLS DEFINING A CAVITY, A FILTER ADAPTED TO CONDENSE VAPORS AND POSITIONED IN SAID CAVITY DIVIDING SAID CAVITY INTO A FRONT PORTION AND A BACK PORTION, A DUCT COMMUNICATING AT ONE END THEREOF WITH SAID BACK PORTION OF SAID CAVITY AND AT THE OTHER END THEREOF ADAPTED TO BE CONNECTED WITH AN EXHAUST FAN, THE IMPROVEMENT COMPRISING: FIRST WALL MEMBERS COMPRISING A FIRST PAIR OF SPACEDAPART SIDE WALLS, A FRONT WALL AND A BACK WALL DEFINING A FIRST OPEN-ENDED NORMALLY CONVECTIVE INSULATING CHAMBER EXTENDING FROM REGIONS INTERMEDIATE THE COOKING APPLIANCE AND THE WALL OF A BUILDING TO REGIONS ADJACENT THE BACK PORTION OF THE CAVITY FOR ALLOWING THE FLOW OF AIR THERETHROUGH BY NORMAL CONVECTION AT A FIRST FLOW RATE; AND SECOND WALL MEMBERS COMPRISING A SECOND PAIR OF SPACED-APART SIDE WALLS AND SAID SECOND PAIR OF SPACED-APART SIDE WALLS, SAID BACK WALL OF SAID FIRST WALL MEMBERS AND THE WALL OF A BUILDING DEFINING A SECOND NORMALLY CONVECTIVE INSULATING CHAMBER SUBSTANTIALLY COEXTENSIVE WITH SAID FIRST NORMALLY CONVECTIVE INSULATING CHAMBER FOR ALLOWING THE FLOW OF AIR THERETHROUGH BY NORMAL CONVECTION AT A SECOND FLOW RATE DIFFERENT FROM SAID FIRST FLOW RATE, AND MEANS FOR CONTROLLING THE AMOUNT OF AIR FLOWING IN SAID SECOND NORMALLY CONVECTIVE INSULATING CHAMBER, AND SAID SECOND FLOW RATE BEING LESS THAN SAID FIRST FLOW RATE.