Spiral pipe, in combination with an assortment of stock round fittings, is an industry standard for quality duct construction. It is possible to select most of the duct and fittings needed for a job from standard components or via catalog, minimizing the need for more expensive custom duct pieces. The flexibility that this approach provides to layout can save the day when precise layout details are not available until installation begins.

The benefits of spiral duct are also seen during ductwork fabrication. Officials with Streimer Sheet Metal Works Inc. of Portland, Oregon, said they believe that spiral is the most efficient means of producing steel air-handling ductwork. Streimer has observed that product efficiencies for fabrication are as high as 3-to-1 as compared with rectangular duct.

Spiral also offers great flexibility in manufacture. One tube-forming machine can produce a variety of products, from less than 4-inches-diameter galvanized duct up to 5-foot-diameter stainless steel ductwork with flanges. Custom lengths are also simple to accommodate, and are much more efficient to produce than custom-length rectangular duct.

Additionally, spiral pipe offers good efficiency in material usage. The ratio of duct length versus material weight used is better than for rectangular duct. Depending upon pressure rating, up to two times less material can be used for the same length of duct with equivalent airflow capability. Streimer said it has has also found that spiral duct scrap levels are significantly lower than or custom-length rectangular fittings.
The ability to nest spiral duct provides great improvements in shipping efficiency for completed duct. Most duct deliveries are limited by available shipping volume. The density of a duct order can be greatly increased by nesting pipe, an option not as easily achieved for ready-to-install rectangular duct.

Installation 

Spiral duct, when used with the proper connectors, can provide additional efficiencies during installation in the field.  Streimer uses the Metu 
MF flange system as the standard joining method for duct diameters greater than 24 inches. The MF flange system yields the following benefits:

• Eliminates the need to access the full circumference of the joints. The flanges are installed via the use of a SR joining clip, which slips over the mating flanges and both seals and secures the pipe joint via one access location. In cramped or high-risk access situations this feature of the MF flange system can greatly simplify a difficult install. 
• Reduces the time to make the connection. The single-bolt clamping system, complete with built-in sealing gasket, can shave hours off of an installation.
• Finished and elegant in appearance as compared to bolted flanges. With today’s trend towards exposed ductwork in construction, the use of a high-quality, uniform connection system like the Metu MF flanges and SR joining clip enhance the finished and professional look of a spiral system.

Operation

Once the project is complete, round duct continues to deliver benefits to customers. Round pipe systems have less heat gain and lower leakage rates than comparable rectangular systems, resulting in lower overall operation costs.
Spiral duct continues to set the standard for efficiency in all phases of a project, from layout through installation. Even after the construction project is complete and the system is live, round spiral duct can deliver optimized and efficient air distribution, officials say. 

This article originally appeared in the January 2016 issue of SNIPS in the SPIDA insert. This article and its images were supplied by Streimer Sheet Metal Works Inc.