Electric heating unit for hot bed

Claim 1

IN AN ELECTRIC HEATING UNIT, A SHALLOW RECTANGULAR FRAME; A SHEET OF HEAT REFLECTIVE MATERIAL FORMING A BOTTOM FOR SAID FRAME; SPACED APART INSULATOR SUPPORTS TRANSVERSELY DISPOSED IN SAID FRAME FLUSH WITH THE TOP PLANE OF SAID FRAME; SPACED APART INSULATORS CARRIED BY SAID INSULATOR SUPPORTS; A TOP PLATE FORMED OF A SHEET OF THIN WATERPROOF HEAT CONDUCTIVE MATERIAL COVERING THE TOP OF SAID FRAME, SAID TOP PLATE BEING CLOSE TO SAID INSULATORS AND RESTING ON AND BEING SUPPORTED BY SAID INSULATOR SUPPORTS; A LAYER OF HEAT INSULATING MATERIAL IN SAID FRAME ON SAID HEAT REFLECTIVE BOTTOM AND SPACED BELOW SAID HEAT CONDUCTIVE TOP PLATE PROVIDING AN AIR CHAMBER BETWEEN SAID INSULATING MATERIAL AND SAID TOP PLATE AN ELECTRIC HEATING ELEMENT DISPOSED HORIZONTALLY IN THE UPPER PORTION OF SAID AIR CHAMBER CLOSE TO SAID TOP PLATE AND EXTENDING BACK AND FORTH IN SAID AIR CHAMBER LONGITUDINALLY OF SAID FRAME AND PASSING THROUGH THE INSULATORS IN SAID INSULATOR SUPPORTS; AND RESILIENT HEATING ELEMENT SUPPORTING DEVICES CONNECTING SAID HEATING ELEMENT WITH THE END WALLS OF SAID FRAME SUPPORTING SAID HEATING ELEMENT AND MAINTAINING THE SAME UNDER TENSION.