How is Spiral Duct Made?

Have you ever found yourself staring at exposed spiral duct work and wonder how it was made? If your answer was no I guess you can stop reading, but it is a pretty interesting process. If your answer was yes, continue reading to find out.

While spiral duct isn’t something we manufacture at Metalwest, HVAC is a common industry we service. So, why not delve into the process behind one of our serviceable industries?


To discover how spiral duct is made we must first cover the basics, or in other words, the materials.

Galvanized Steel

Galvanized steel is the most common material used for ductwork. Galvanized steel is ideal for ductwork because it is corrosion resistant and can withstand higher temperatures.


Aluminum sheet is used for ductwork because of its high strength and light weight. Lightweight pieces of duct can span longer distances without the need for supports. It is also flexible, which means it can be stretched and bent multiple times, but still hold an airtight seal.

Stainless Steel

Stainless steel ductwork is used more frequently in laboratories due to its sanitary benefits as well as its corrosion resistance to harsh substances. It also has greater strength than aluminum and is abrasion resistant.

The Spiral Duct Process

There are three parts to the spiral duct process. The first starts with the mill and the making of the raw steel (here are some posts on how galvanized, aluminum, and stainless steel are made).

The second part consists of Metalwest receiving coils from the mills and processing them into slit coils. Slit coils are narrower coils cut from a larger master coil (you can read more about it here).

These slit coils are sent to customers per the required specifications and processed into spiral duct, bringing us to the third part of the process.

The Spiral Duct Fabrication Process

Once a customer receives the slit coil it is placed on an uncoiler and sent through a rough leveler to flatten the material. It is then sent through an edge trimmer and formed.

The forming process sends the strip through an inner and outer welding stage that moves it in a circular motion to form a spiral. The edges are welded or pinched together to form the duct piece. It is then cut from the machine at the desired length, inspected, tested, and then sent on be installed.

Here is a video example of the spiral duct process.

The finished spiral duct (in some cases it goes on to be painted) is then installed in commercial buildings such as warehouses, medical facilities, restaurants, schools, etc. So the next time you find yourself staring at exposed ductwork while sipping on a caramel macchiato, you will know how it was made.

For more information about the materials used for spiral duct contact your local sales representative.