Pros and Cons of Spiral Ductwork

Spiral Ductwork vs Clamp-Together Ductwork

Spiral duct has been around a long time and if you have used it regularly, you are likely comfortable with the benefits—or at least the apparent benefits of spiral duct for industrial applications. US Duct has received a number of inquiries from contractors and reps looking for something to substitute for traditional spiral duct for such applications as dust, fume, mist and particle collection. As we have worked through these conversations, we have discovered several reasons that—when considering the entire job—Clamp-Together Duct might just be a better solution.

Spiral duct is an often specified and commonly known duct pipe style. As the name implies, the duct is formed by spiraling and locking strips of metal together to form a continuous piece. This forming method enables the manufacturer to produce various lengths of duct in less time, creating a duct that is typically less expensive than duct formed by rolling sheets. Yet, when considering ductwork options for your customers and looking at the entirety of the project from design, manufacturing, shipping, installation and ongoing maintenance, spiral duct may not be the best solution. Consider the information below and the possible alternative of Clamp-Together Duct as a better solution.

Consider the information below and the possible alternative of Clamp-Together Duct as a better solution.

As with many products that look cheaper on the surface, there are hidden costs associated with spiral AND hidden benefits from other types of ducts, as the chart above indicates. Consider these facts prior to ordering.

1. Spiral duct typically comes in lengths that are not conducive to handling, especially in larger sizes. While the long length may appear to provide faster installation, the truth is that the difficulty of maneuvering it into place increases exponentially with length. The difficulty of loading and unloading spiral duct from trucks increases with length as well.
2. Spiral duct can be joined by various methods. None of them are easy.
   1. Flanges/Angle Rings- The problem with this process is that spiral duct is formed by locking edges of the metal together. This creates spirals of 4 thicknesses of metal.  This thickness makes it virtually impossible to turn a van-stone edge (a ~1/2’ edge that is turned back at 90 degrees to the duct) or to compress the van-stone ends between the flanges.
   2. Flanges can be welded on- but only if the spiral is of sufficient gauge AND the installer is good at welding lighter gauge metal.
   3. Crimping- This method involves crimping one end and forcing it into the adjoining piece. The joint is then taped or screwed together in order to hold it together. This is neither easy nor effective in making a tight fit. It also requires exact measuring and if screws are used, leave protrusions into the duct.
   4. Using collars. The collars are typically made to slide into the ends of the joining duct. Not only are these collars expensive, but they also require tape or screws to hold them together. Additionally, this leaves a protrusion in the duct. Big end/small end collars eliminate this by allowing the collar to be slid into one duct and over the other (in the direction of the airflow) but these are even more expensive- and still require tape or screws.
   5. Spiral fittings (elbows, branches, etc.) can be made with big end/small end connections and eliminate using collars when joining fittings to the straight duct but collars are still necessary for joining straight duct. Both fittings and straight duct also require tape or screws to secure the connections.
   6. In all instances above, exact cuts are required. And while the straight duct is cheaper, the branches, elbows and other fittings are no cheaper than other systems.
3. Clamp-Together Duct pipe is more expensive than spiral duct but usually, the difference in price is only in the straight duct. The fittings are approximately the same price. The clamps do add cost to the system but only in the metal product. They are actually part of the reason for reducing the installation costs of the project.

Download our e-book here to learn more.