Reference
Definition
What the word means. This is not a work instruction.
Rectangular duct is box-shaped and commonly uses S-and-drive, TDC, TDF, or Ductmate-style transverse joints. Round and spiral duct are circular and usually connect with slip couplings, collars, bands, screws, gasket, sealant, or flanged rings depending on the job.
Rectangular duct is often easier to route tight to structure. Spiral is clean, strong, and common in exposed or open-ceiling areas.