Glossary of ductwork terms

A
Air handler unit (AHU)
Often attaches to the duct system. The AHU is usually a large metal box made of galvanized sheet metal containing a blower, heating or cooling elements, filter racks or chambers, sound attenuators, and dampers.

Angle boot
Used for connecting a round pipe to a wall stack duct and fittings.

C
Crimped joint
Two pieces of galvanized steel or other ductile material that are deformed to hold one another.

D
Dampers
Dampers are installed to regulate airflow. Dampers for commercial use include Air Measuring, Thermal, Backdraft, Industrial/Heavy Duty, Tunnel Transit, Marine, Balancing, Low Leakage, Relief, and Zone.

Duct fittings
Duct fittings and configurations, including ells, tees, and reducers, are responsible for equalizing the duct pressure and balancing the airflow. For example, a reducer is a fitting that’s used when a change from one size duct to another size is needed.

E
End boot
Used for right-angle centre-end transition from round pipe or insulated flexible duct to a register or grille.

O
Outlets
Outlets including diffusers, grilles, and registers, divide the airflow in a truck-and-branch ductwork design. For example, diffusers are used to introduce conditioned air into a space to achieve even distribution and mixing with minimum noise.

P
Panning
Flat metal nailed to joists for return air.

Plenum
The central distribution and collection airflow unit for an HVAC system.

R
Radial plenum
Also called extended plenum design is when air supplies and returns have direct connections to the HVAC unit. A trunk-and-branch or central plenum design has supplies and returns branch off from a long “trunk” directly connected to the unit. The latter is mainly used for residential.

Reducer
Rectangular, round, or square galvanized steel used to increase or decrease pipe size.

Register box
Also known as a floor box, which is a galvanized steel grille with moving parts that’s capable of being opened and closed with the airflow directed.

Return plenum
Used to carry air from several large return grilles to a central air handler.

S
Smoke & Fire Dampers
Used to seal off a duct when they detect smoke and fire.

Spin-in starter
Provides a secure attachment point for a new HVAC duct.

Stack head
Used to create a transition from a stack duct to a register and allows ducting to fit between 2- and 4-inch wall studs.

Supply plenum
Used to direct air from the central unit to the rooms which the system is designed to heat or cool.

Take-offs
Carefully designed round, oval, or rectangular fittings used to take the correct amount of airflow from the main duct into each branch duct.

Termination cap
Galvanized steel used to terminate a round pipe run.

Turning vanes
Used to minimize air turbulence and help airflow at sharp changes of direction.

Vents
Typically placed in the ceiling with their edges corresponding to the opening in the above duct. As warm or cool air pours through the commercial ductwork, vents allow it to disperse into the rooms below.

Vent cap
Provides protection for the open end of a ductwork vent stack. Each fitting and configuration helps the overall commercial ductwork performance.

Vertical ducts
Also called stacks, they allow air to travel vertically within relatively thin. walls.

Volume control dampers
Used to enable the volume of airflow to be adjusted.