Fireplace flue construction

Claim 1

A PREFABRICATED FIREPLACE CONSTRUCTION COMPRISING: (A) WALLS FORMING A SOLID-FUEL BURNING FIREBOX, MEANS FORMING A DRAFT OPENING IN SAID FIREBOX, SHEET METAL WALLS FORMING A SMOKE CHAMBER EXTENDING UPWARDLY FROM SAID FIREBOX AND HAVING A LOWER PART COMMUNICATING WITH SAID FIREBOX DRAFT OPENING AND AN UPPER PART, (B) AN UPWARDLY EXTENDING FLUE PIPE HAVING AN UPPER EXHAUST END AND A LOWER END, SAID PIPE LOWER END BEING OF SMALLER CROSS-SECTIONAL AREA THAN SAID SMOKE CHAMBER UPPER PART AND FORMING A COMMUNICATING JUNCTION WITH SAID SMOKE CHAMBER UPPER PART FOR DRAINING SMOKE AND COMBUSTION FUMES THEREFROM, (C) AN UPWARDLY EXTENDING SECONDARY SLEEVE SURROUNDING AND SPACED FROM SAID FLUE PIPE AND FORMING A COAXIAL SECONDAR CONDUIT THEREWITH, SAID SECONDARY SLEEVE HAVING AN UPPER EXHAUST END AND A LOWER MOUTH, SAID SECONDARY SLEEVE MOUTH OPENING EXTERIORLY OF SAID SMOKE CHAMBER ADJACENT SAID SMOKE CHAMBER UPPER PART FOR RECEIVING HEATED AIR GENERATED ON THE EXTERIOR OF SAID SMOKE CHAMBER UPPER PART. (D) WALLS FORMING AN OUTER SHELL SPACED OUTWARDLY FROM SAID FIREBOX AND SAID SMOKE CHAMBER FORMING THEREWITH AIR CURRENT PASSAGEWAYS MEANS FORMING LOWER INTAKE DRAFT OPENINGS, IN SAID OUTER SHELL AND COMMUNICATING WITH SAID AIR CURRENT PASSAGEWAYS, (E) SAID OUTER SHELL HAVING AN UPPER PART SPACED GENERALLY UPWARDLY FROM SAID SMOKE CHAMBER UPPER PART AND SUBSTANTIALLY SURROUNDING SAID SECONDARY SLEEVE MOUTH, AND (F) AN UPWARDLY EXTENDING OUTER SLEEVE SURROUNDING SAID SECONDARY SLEEVE AND SPACED THEREFROM FORMING AN OUTER CONDUIT THEREBETWEEN, SAID OUTER SLEEVE HAVING AN UPPER EXHAUST END AND A LOWER INTAKE END, SAID OUTER SLEEVE INTAKE END COMMUNICATING WITH SAID OUTER SHELL UPPER PART FOR RECEIVING HEATED AIR FROM SAID AIR CURRENT PASSAGEWAYS, (G) WHEREBY SAID OUTER SHELL AND OUTER SLEEVE REMAIN RELATIVELY COOL DURING SEVERE FIRE CONDITIONS IN SAID FIREBOX.