Abstract: A substantially airtight ducting enclosure is provided for a heating, ventilation, and/or air conditioning system. The enclosure, which may be a register box for return air or supply air, has a body formed from at least one planar sheet, the body having an inlet and an outlet. At least one of the inlet and the outlet is formed by folding corners of the planar sheet to form planar sides that lie in intersecting planes. The enclosure is then mounted to a surface of an interior area of a structure, and connected to ducts for communicating air between the interior area and a central air-handler unit.

Abstract: A sheet-metal elbow is coupled by direct attachment to a flat sheet-metal air inlet panel of an air distribution boot or register box by roll-formed flange portions that are mated in interlocking, overlapping engagement with each other. The air inlet panel includes an outwardly flared coupling flange bordering an air inlet opening. The neck of the sheet-metal elbow includes a folded coupling flange that is dimensioned for interfitting, overlapping engagement with the outwardly flared elbow coupling flange. The coupling flanges are clasped together by a hydraulic ram that drives an expandable mandrel into a V-shaped die cavity. The tightly clasped, overlapping flange portions permit smooth, continuous rotation of the elbow through 360.degree. with respect to the register box for alignment with a branch conduit. The interlocked flanges also provide a strong mechanical union that is virtually leak-free under normal ventilation air flow conditions.