How to fabricate and install sheet metal ventilation ducts?

Fabricating and installing ventilation ductwork in sheet metal is a core skill of the tinsmith-sheet metal worker:

Materials:

• Rectangular ducts: galvanized steel 26 to 22 gauge (depending on size). Larger ducts require thicker sheet metal
• Round ducts: galvanized steel 28 to 24 gauge, formed on a rolling machine
• Kitchen exhaust ducts (grease): stainless steel or black steel, minimum 18 gauge

Fabrication:

• Rectangular ducts are formed using a brake to create longitudinal bends
• Joints are made using Pittsburgh locks — the standard joint for rectangular ducts
• Flanges at the ends allow joining sections together with bolts and duct tape

Installation:

• Ducts are suspended from the ceiling using threaded rods and supports every 1.2 to 2.4 meters depending on diameter
• Duct sections must be airtight — using UL 181 certified tape or mastic
• Insulated ducts (flexible or rigid) are used for thermal systems