Abstract: An apparatus for converting a conventional rectangular HVAC duct to a flat oval shaped duct where a conventional rectangular duct fitting is provided with a converting means to convert the opening from rectangular to a flat oval. The converting means is formed by a pair of arcuate members defining semi-circular edges and having recesses to receive portions of parallel members. The apparatus utilizes two sheet metal pieces which are formed in arcuate contours that connect between flat edges of parallel sheets to form the oval shape.

Abstract: A method and structure for the integral reinforcement of HVAC ducting including the steps of laying out one or more planar sheet metal blanks having portions defined therein dedicated for integral rib reinforcement; placing relief slots in the dedicated portions of the blank corresponding to the seams and folding lines; forming the integral reinforcement rib from the dedicated blank material; bending the blanks along fold lines and assembling the rectangular duct; and placing rib corners over the reinforcing rib ends at the corners of the duct. Alternatively, the step of cutting the reinforcing rib at the fold lines may be substituted for the step of placing slots in the blank. The completed structure includes reinforcing ribs circumferentially positioned around the duct or on the planar duct surfaces, the ribs being formed of, and integral to, the duct itself. Pre-manufactured rib corners serve to seal and strengthen the reinforcement ribs as required.