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A frost resistant, horizontal folding door for a freezer room has heater assemblies in the header, jambs and for simultaneously heating the door curtain and the floor of the doorway. The heater assembly in the header can be a mat of open mesh fiber glass having a serpentine array of an electric resi

A frost resistant, horizontal folding door for a freezer room has heater assemblies in the header, jambs and for simultaneously heating the door curtain and the floor of the doorway. The heater assembly in the header can be a mat of open mesh fiber glass having a serpentine array of an electric resistance heating wire bonded to it. The heater assembly in the jamb can be a formable electrical resistance heater within the structure of the jamb. The heater assembly, for the door curtain and the floor of the doorway can be an electrical radiant heater disposed on the header and directed at the curtain and the floor.

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A foldable door comprising: a header including a front, generally vertical panel and a rear, generally horizontal panel, said header being disposed along a top of an associated doorway; a downwardly depending foldable curtain disposed below said header; curtain supporting means connected to said hea

A foldable door comprising: a header including a front, generally vertical panel and a rear, generally horizontal panel, said header being disposed along a top of an associated doorway; a downwardly depending foldable curtain disposed below said header; curtain supporting means connected to said header and movably supporting said curtain for movement between a closed, extended position and an open, folded position in which an upper edge of said curtain is in close proximity to said rear panel, said supporting means including a generally C-shaped bracket for receiving a plurality of carriages associated with said curtain; a pair of hollow jambs disposed along opposite sides of said doorway, each of said jambs having an inwardly directed, cantilevered hinge mounted thereon in opposing positions at either side of said doorway, said curtain supporting means being pivotally mounted on each of said hinges, each of said jambs including an internal chamber having an interior wall; means for simultaneously raising both a surface temperature of said foldable curtain and a temperature at the floor level of said doorway above a frost formation temperature; jamb temperature raising means disposed on said interior wall within said chamber of said jambs for raising a temperature of at least one of said jambs above the frost formation temperature, said jamb temperature raising means comprising: a serpentine jamb heating element disposed on said interior wall of said jamb; a first thermal insulating layer disposed over said jamb heating element; and first retention means for securing said first thermal insulating layer and said jamb heating element to said interior wall; front panel temperature raising means disposed within said header for raising the temperature of said front panel above the frost formation temperature, said front panel temperature raising means comprising: front panel heat transferring means disposed on an interior surface of said front panel for transferring heat to said front panel; a second thermal insulating layer covering said front panel heat transferring means; and second retention means for securing said second thermal insulating layer and said front panel heat transferring means to said front panel; and rear panel temperature raising means disposed within said header for raising the temperature of said rear panel above the frost formation temperature, said rear panel temperature raising means comprising: rear panel heat transferring means disposed on an upper face of said rear panel for transferring heat to said rear panel; a third thermal insulating layer covering said rear panel heat transferring means; and third retention means for securing said thermal insulating layer and said rear panel heat transferring means to said interior face.