Hot air furnace with improved heat exchanger construction

Claim 1

A process of securing at least one plate member to at least one heat exchange unit of a hot air furnace, comprising providing at least one forwardly extending mounting flange on each of said heat exchange units defining an opening therein, forming openings in said at least one plate member congruent with said heat exchange unit openings, providing sheet insulating material substantially coextensive with said plate member, forming openings in said sheet insulating material substantially smaller than said heat exchange unit openings positioning sheet insulating material and said at least one plate member over said heat exchange unit with said insulating material interposed between said plate member and heat exchange unit, arranging said openings formed in said plate member in alignment with the openings defined by said mounting flanges on said heat exchange units arranging said insulating material openings covering a substantial portion of the openings defined by said mounting flanges on said heat exchange units but exposing a concentric portion of each said heat exchange unit opening, effecting relative movement between each said plate member and heat exchange unit so as to urge each of said mounting flanges through the corresponding apertures in said plate member to thus cause the portion of said insulating material overlying the flange defined openings to form a sleeve on the outer surface of said flange, thereafter expanding said flanges into a plate parallel with that of said plate member to thereby secure said plate member to said heat exchange unit with said insulating material therebetween and effect a leakproof joint between said plate member and heat exchange unit.