What seam is used to attach a round collar to the side of a rectangular duct?

The seam that is commonly used to attach a round collar to the side of a rectangular duct is recognized as the spin-in seam. This technique involves inserting the round end of the collar into a specially constructed opening on the rectangular duct. The circular part is then rotated and held in place, allowing for a secure connection without requiring extensive tools or mechanical fastening.

The spin-in seam is particularly suitable for this application because it provides a tight fit, reducing potential air leakage while maintaining structural integrity. This design optimally accommodates the difference in shapes, ensuring an efficient transition between the duct forms. Additionally, if executed properly, this seam type can simplify installation, making it a favored method among HVAC professionals when connecting different duct shapes.

In contrast, other seam types serve different functions or applications, such as reinforcing joints or allowing for expansion and contraction, which makes them less suitable for the specific task of attaching collars to ducts.