Ductwork Fabrication and Installation: A New Sheet-Metal Hand's First Week
Sheet-metal gauges, S-cleats and drives, hanging trunk and branch duct, and what a new HVAC helper actually does.
Table of contents
What the work looks like
Ductwork is the sheet-metal network that moves heated and cooled air from the air handler or furnace to the rooms it needs to condition. As a new HVAC helper or sheet-metal apprentice you will hand-fabricate and install galvanized steel, aluminum, or flexible duct, assemble fittings in a shop, cut and seam rectangular duct with hand tools and a Pittsburgh machine in a fab shop, and hang trunk lines and branch runs in attics, basements, crawl spaces, and commercial ceiling plenums.
Job titles: HVAC Helper, Sheet Metal Apprentice, Duct Installer, Tinner. Apprentice wages $18 to $26 per hour; SMART (Sheet Metal Workers) union journeyman rates $38 to $55 plus benefits. Non-union shops run lower. Commercial new-construction and service are the two main paths.
Safety and tools
Sheet-metal edges are sharp. The number-one injury in this trade is a cut hand. Work gloves (Kevlar or mechanic's cut-resistant) stay on. Eye protection stays on. Sleeves stay down. Long pants, boots, and a hard hat on commercial sites are required.
Common gauges:
- 30 gauge (thinnest): residential branch runs up to about 10 inches.
- 26 gauge: residential trunk and small commercial.
- 24 gauge: commercial trunk up to about 30 inches.
- 22 to 16 gauge: larger commercial and industrial.
Joints and fittings: S-cleats and drives for rectangular transverse joints (slide, hammer, tack), TDC/TDF flanges with gasket and cleat for larger duct, snap-lock or button-lock for round duct, and flex duct with zip ties and mastic at the collar. Seal seams with UL-181 mastic or foil tape (never cloth duct tape on HVAC).
Tools: aviation snips (red for left cuts, green for right, yellow for straight), Pittsburgh hand seamer, rivet gun, hand brake for shop bends, Wiss notcher for S-cleat drops, tin-snip gauge, measuring tape, Sharpie, chalk line, laser level for hanging trunk, impact driver and 3/8 hex bits for screws, strap or trapeze hangers for commercial.
Safety: ladder work and overhead duty. Three points of contact on the ladder. Do not overreach. Use a lift when the ceiling is over 10 feet. OSHA fall protection above 6 feet on commercial sites.
Your first exercise
In a home or building you know, look up at the ductwork (attic, basement, mechanical room, or exposed warehouse ceiling). Identify the trunk (big rectangular duct off the air handler), the takeoffs (smaller branches coming off the trunk), the supply boots where branches meet registers, and the return duct (usually one large panned-joist run or a big trunk back to the furnace). Estimate duct size from the outside. Notice how the duct is hung (straps, hangers, or rod-and-trapeze).
That mental picture is the job: trunks, branches, boots, returns, and how they hang.
Where to go next
Build on Ductwork Fabrication with HVAC Fundamentals (Introduction to HVAC), Refrigeration Systems (Introduction to Refrigeration), HVAC Controls and Thermostats (Introduction to HVAC Controls), Gas Furnace Service (Introduction to Gas Furnace Service), and Heat Pumps (Introduction to Heat Pumps). Safety: Workplace Safety, Ladder Safety, Confined Space Entry (Introduction to Confined Space Entry).