How do sheet metal contractors join duct sections in a Toronto residential installation?

Sheet metal contractors in Toronto join duct sections using a combination of mechanical seams, fasteners, and sealants that create airtight, durable connections designed to withstand decades of temperature cycling and vibration from the HVAC system. The specific joining method depends on whether the duct is round or rectangular, and whether the connection is a factory fitting or a field-fabricated joint.

For rectangular ductwork, the most common joining method in GTA residential installations is the drive cleat and S-cleat system. Two opposite sides of the duct section end in S-shaped folded edges (S-cleats) that slip over the mating section's raw edge, while the other two sides use drive cleats — flat metal strips bent into a channel shape that are hammered onto the overlapping duct edges to lock them together. This creates a rigid mechanical connection without welding. Another common method is the Pittsburgh lock seam, where one duct section has a pocket fold that the other section's edge slides into and is then bent over to create a permanent, self-locking joint. Pittsburgh seams are stronger than cleat connections and are standard for trunk line fabrication in quality GTA sheet metal shops.

For round ductwork, sections are joined using crimped ends and slip connections. One end of each duct section is crimped (reduced slightly in diameter using a crimping tool) so it slides inside the next section. The overlap is typically 1.5 to 2 inches, and the joint is secured with three or more sheet metal screws evenly spaced around the circumference. Spiral duct uses beaded slip couplings — external sleeves that fit over the joint between two duct sections and are secured with screws and sealed. These couplings create a clean, strong connection with minimal air leakage.

Mechanical fastening is required at every joint regardless of the connection method. Sheet metal screws (commonly #8 or #10 hex-head self-drilling screws, often called TEK screws or zip screws) are driven through overlapping metal at joints and fittings. The Ontario Building Code requires mechanical fastening at all duct connections — sealant alone is never sufficient. Rivets are used where screw heads would protrude into the airstream or where a cleaner appearance is desired, particularly on exposed spiral duct installations.

Sealing is the critical final step and the one most commonly skipped or done poorly in budget GTA installations. After mechanical fastening, every joint, seam, and connection point must be sealed with duct mastic (a thick, water-based paste applied with a brush or gloved hand) or UL 181-rated foil tape. The best practice, and what quality GTA contractors do, is a belt-and-suspenders approach — mastic applied generously over the joint, then foil tape over the mastic for reinforcement. Grey cloth duct tape, despite its name, is never acceptable for sealing HVAC ductwork because it dries out and fails within two to five years in Toronto's temperature extremes.

Unsealed joints are the single biggest source of energy waste in residential duct systems. A typical older GTA home with unsealed ductwork loses 20 to 30 percent of conditioned air through joint leaks before it reaches living spaces. When hiring a ductwork contractor, ask specifically about their sealing practices — a contractor who seals every joint with mastic and foil tape is demonstrating the attention to detail that separates quality work from cut-rate installations.