Choosing the Right Duct System for Your Building: Five Types Explained

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The duct system is a network of tubes that guide air from one location to another inside a building's walls, floors, and ceilings...

The duct system is a network of tubes often made through metal fabrication that guide air from one location to another inside a building’s walls, floors, and ceilings. The characteristics of each type of duct material can make them useful in specific applications, and improper ductwork installation can result in inefficiency and increased costs. That’s why it’s important to understand the types of ductwork. Learn more about each material, its uses, pros and cons.

1. Flexible Duct

This type of ductwork is made for HVAC system applications and is called flex duct. Typically, they consist of a flexible plastic inner liner supported by a metal helix wire coil on the inside. Ducts are normally insulated with fiberglass.

Although flexible ductwork is typically installed in a single continuous piece, there is the possibility of a leak at the seam when it is connected to rigid sheet metal ductwork. To prevent a restriction in air flow, flex ducts should be installed properly and carefully. Incorrect installation of a flexible duct system can result in tearing, sagging, sharp bends, kinks, and crimping, which can lead to service problems and possible equipment failure.

2. Galvanized Steel

Perfect for sustainable buildings, sheet metal ductwork like galvanized steel (and aluminum, which we’ll cover next) are created from recycled materials and easy to clean. Sheet metal has a number of other advantages: it is sturdy, non-combustible and non-porous. Due to this non-porous material, sheet metal ducts restrict the growth of mold.

Galvanized steel, used as a duct material for most air handling systems, is high-strength, durable, rust-resistant, widely available, easily changed to a new shape and able to weld with similar materials. Round ducts are recommended for maximum air-carrying capacity rather than rectangular ducts, and they have lower installation costs, which may result in substantial cost savings. (Rectangular ducts are most flexible when it comes to fitting within limited spaces.)
A disadvantage of sheet metal ductwork is they are more likely to leak air where seams or two sections are joined.

3. Aluminum

Most commonly used for cleanroom applications, aluminum ducts are light in weight and easy to install. These ducts have a resistance to corrosion from moisture, but the basic cost per pound is more than galvanized steel.
Limiting characteristics of aluminum ductwork include its low strength, cost of materials, thermal expansion and weldability.

4. Fiberglass Ductwork

Often, fiberglass ducts are used in low-pressure systems. In sheet metal ducts, fiberglass insulation with a metal foil is often used as a vapor barrier. It serves as an insulation material to prevent condensation.

Fiberglass ducts are insulated as part of their construction, and their applications include underground duct systems.
The advantages of fiberglass ducts are their resistance to corrosion, strength, and ease of modification. Fiberglass duct board provides excellent sound attenuation, reducing sounds created by an HVAC system, which is ideal for commercial buildings.

5. Fiberboard Ductwork

This type of rigid ductwork is constructed of fiberglass stands bonded by resin. The exterior surface of the board is covered with foil, acting as an air and moisture barrier; the interior surface of the fiberboard — in contact with air flow — is not as smooth as metal. Fiberboard ductwork is often used for heating and cooling ducts, but it is not recommended for ventilation ducts.
One advantage of this type of ductwork is that fiberboard is inherently insulating. Fiberboard ductwork is airtight, contingent on the care taken in constructing the sections and cutting and sealing the joints and seams. An unnoticed crack in the bonded fiberglass over time can lead to erosion of the glass fibers, creating a durability issue and compromising the insulation value of the duct.


These five types of air duct systems can be used to determine which type of ductwork is right for your building. Even though a duct system is simple in appearance, it is important to the comfort and efficiency of a building. Do you need Auckland sheet metal fabrication services for your existing building or new construction? Contact Hammer Metalworks to work with our expert sheet metal fabricators.