What gauge sheet metal is used for residential ductwork in the GTA?

Residential ductwork in the GTA is typically fabricated from 26-gauge or 28-gauge galvanized sheet metal for branch runs, and 24-gauge or 22-gauge for trunk lines and plenums. The gauge number is inversely related to thickness — lower gauge numbers mean thicker, stronger metal. Choosing the correct gauge for each part of the duct system affects durability, noise, rigidity, and long-term performance.

For trunk lines — the main rectangular or round ducts that carry conditioned air from the furnace plenum to branch takeoffs — 24-gauge galvanized steel is the standard across GTA residential installations. Trunks on larger homes or those spanning longer distances may use 22-gauge for additional rigidity and to prevent oil-canning, which is the annoying popping or booming sound that occurs when thinner metal flexes under pressure changes as the blower cycles on and off. If you hear your ductwork banging or popping when the furnace starts, undersized gauge on the trunk line is often the culprit.

Branch runs — the smaller round ducts running from the trunk to individual room registers — are typically 28-gauge for ducts 8 inches in diameter or smaller, and 26-gauge for ducts larger than 8 inches. These thinner gauges are adequate for shorter runs with lower airflow volumes, and they are easier for contractors to cut, crimp, and connect in tight residential spaces like joist bays and wall cavities.

Plenums and return air boxes are usually fabricated from 22-gauge or 24-gauge galvanized steel because they are large, flat panels that are prone to flexing and oil-canning under the static pressure created by the blower. Heavier gauge metal resists this movement and reduces noise. Custom plenums fabricated by GTA sheet metal shops typically use 22-gauge as standard.

The Ontario Building Code and SMACNA (Sheet Metal and Air Conditioning Contractors' National Association) standards specify minimum metal thicknesses based on duct dimensions and pressure class. Residential systems operating at low pressure (up to 1 inch water gauge) follow the gauges described above, which are well-established across the GTA market. Some production home builders use 28-gauge for trunk lines to save material costs, which meets minimum code requirements but produces noisier, less durable systems — this is one area where builder-grade quality often falls short.

When getting quotes for ductwork in the GTA, ask your contractor what gauge they use for trunks versus branches. A contractor using 24-gauge trunks and 26-gauge branches is following best practice. If they are using 28-gauge throughout, you may experience more noise and the ductwork will be more susceptible to damage and denting over its lifespan. Material costs for stepping up one gauge are modest — typically $200 to $500 more for an entire residential system — but the improvement in durability and noise reduction lasts decades. Find experienced sheet metal contractors through the Toronto Construction Network directory for quotes on your ductwork project.