Prefabricated metal chimney

Claim 1

A PREFABRICATED DOUBLE WALLED CHIMNEY SECTION ADAPTED TO BE COUPLED TO A SIMILAR SECTION TO FORM A CHIMNEY COLUMN, SAID SECTION COMPRISING: (A) AN INNER PIPE; (B) AN OUTER PIPE; (C) INSULATION BETWEEN SAID PIPES; (D) A MALE COUPLER ON THE UPPER END, AND A FEMALE COUPLER ON THE LOWER END OF SAID SECTION, SAID COUPLERS COMPRISING (E) ANNULAR RADIAL PLATES WITH INNER AND OUTER GENERALLY AXIALLY EXTENDING FLANGES CONNECTED TO SAID INNER AND OUTER PIPES FOR RETAINING THE SPACING BETWEEN THEM; (F) SAID INNER AND OUTER FLANGES OF SAID MALE COUPLER BEING RIGIDLY CONNECTED TO THE UPPER ENDS OF SAID INNER AND OUTER PIPES, RESPECTIVELY; (G) SAID OUTER PIPE BEING RIGIDLY CONNECTED TO SAID FEMALE COUPLER OUTER FLANGE AT ITS LOWER END, AND SAID INNER PIPE EXTENDING CLOSELY ADJACENT NEAR ITS LOWER END TO SAID FEMALE COUPLER INNER FLANGE AND BEING MOVABLE RELATIVE THERETO, SAID INNER PIPES OF SUCCEEDING SECTIONS EXTENDING DOWN INTO THE INNER PIPE OF THE NEXT LOWER SECTION AND BELOW SAID PLATE; (H) MEANS FOR SPACING SAID PLATES OF ADJACENT COUPLERS APART BY A PREDETERMINED AMOUNT TO PROVIDE A FIXED ANNULAR AIR SPACED BETWEEN ADJOINING SECTIONS; (I) AND MEANS ON SAID MALE AND FEMALE COUPLERS FOR AXIALLY LOCKING SAID SECTION TO AN ADJOINING LIKE SECTION.