Ductwork is the network of sheet metal, flexible or other ducts that carries air through a building as part of the heating, ventilation and air conditioning (HVAC) system. Ducts are typically round, rectangular or flat oval, and are hung from the structure above with rods, straps or support angles. They can be insulated on the outside to control heat loss and condensation, or lined on the inside to reduce noise.
Ductwork connects equipment such as an air handling unit, rooftop unit or fan coil unit to the grilles and diffusers in each room.
What ductwork does
- Supply air: carries conditioned air from the equipment to occupied spaces.
- Return air: brings air back to the equipment to be filtered and reconditioned.
- Exhaust: removes air from washrooms, kitchens, labs and parking garages.
- Outside air: brings in fresh air for ventilation.
Types of ductwork
| Type | Where it is used | Notes |
|---|---|---|
| Galvanized sheet metal, rectangular | Main runs in commercial buildings | Fits tight ceiling spaces |
| Spiral round and flat oval | Mains and branches, exposed ceilings | Efficient airflow, clean look |
| Flexible duct | Short connections to diffusers | Keep runs short and stretched to limit pressure loss |
| Fiberglass duct board | Some residential and light commercial | Built-in insulation |
| Fabric duct | Warehouses, gyms, open spaces | Distributes air along its length |
| Stainless, aluminium or plastic | Kitchen, lab, pool and corrosive exhaust | Material set by the exhaust type and code |
Ductwork components
- Fittings: elbows, tees, transitions, turning vanes.
- Dampers: volume dampers for balancing, fire dampers and smoke dampers at rated walls and floors.
- Terminal units such as VAV boxes, and grilles, registers and diffusers.
- Access doors for dampers and cleaning; see access panel.
- Flexible connectors at fans to limit vibration.
Installation and QA tips
- Coordinate early. Ductwork is usually the largest service in the ceiling, so it is often routed first in BIM coordination with sprinklers, cable tray and plumbing.
- Install hangers and supports to the specification, which often references SMACNA standards.
- Seal joints to the specified class and leakage-test where required before ducts are insulated or concealed.
- Cap open duct ends during construction to keep out dust and debris.
- Install fire dampers to the manufacturer’s listing, with access for inspection and reset.
- Complete testing and balancing before handover and record final airflows.
Related terms
Related templates and guides
- Ductwork symbols AutoCAD blocks
- Ductwork installation productivity monitoring form
- HVAC design quality checklist
- Introduction to mechanical and electrical systems
Frequently asked questions
What are the main types of ductwork?
The main types are galvanized sheet metal (rectangular, round spiral and flat oval), flexible duct, fiberglass duct board and fabric duct. Stainless steel, aluminium and plastic ducts are used for special exhaust. Commercial buildings mostly use sheet metal, with short flex connections to diffusers.
Is ductwork part of HVAC?
Yes. Ductwork is the distribution part of an HVAC system. Equipment such as air handlers, furnaces and fans condition and move the air, and the ducts carry it to the rooms and back again, along with exhaust and outside air.
Why is ductwork insulated or lined?
Insulation reduces heat gain or loss and stops condensation forming on cold supply ducts. Internal acoustic lining also reduces fan and air noise. The specification says which ducts get external wrap, internal lining or neither.
What is SMACNA?
SMACNA is the Sheet Metal and Air Conditioning Contractors’ National Association. Its HVAC duct construction standards are widely referenced in North American specifications for duct gauges, reinforcement, joints, sealing and hangers.
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