The Spiral Duct Manufacturers Association, better known as SPIDA, is an organization focused on promoting the use of spiral-seam round and flat oval in ductwork fabrication.

The organization itself comprises over 90 member companies — and growing — from all corners of the United States and Canada. For the most part, these members represent manufacturers, contractors and suppliers to the HVAC construction industry. SPIDA’s continuous goal is to promote the use of spiral duct and flat-oval duct through research, testing and education. 

The regular operations and projects of SPIDA are carried out by its board of directors and committees. The people sitting on the board and committees are all from the industry, and volunteer their time and resources to ensure the promotion and use of spiral duct in North America. 

Become a member

SPIDA’s dues are structured to allow companies to choose the appropriate level of participation:

  • Companies that want to support research and testing efforts and have a leadership role in the organization join as a Brad Thomas research contributor and pay $1,100 per year.
  • Companies that are less involved, but want access to the specialized information published by SPIDA and the opportunity to participate in meetings become Industry Supporters and pay $575 per year.
  • Vendors and suppliers may join for $350.
  • The specific benefits vary according to membership level. For more information on SPIDA, please visit, call (803) 732-5818 or follow them on LinkedIn.

Each year, SPIDA hosts a general membership meeting in conjunction with the annual AHR Expo, as well as an annual springtime conference at a unique venue. The general membership meeting is held on the day before AHR Expo begins and is attended by most of the manufacturers in the spiral duct industry. The program consists of a speaker on an important industry or business topic, as well as an update on SPIDA’s efforts in testing and research. 

The next general membership meeting will be held Jan. 29, the day prior to the 2017 AHR Expo show in Las Vegas. 

SPIDA also holds an annual meeting every spring. From April 22-23, association members gathered in Portland, Oregon. The meeting featured guest speakers, roundtable discussions, vendor displays and networking opportunities. It also provided a chance for attendees to enjoy the city by taking part in a boat cruise, wine tour and dinner overlooking the city. 

Research focus 

The backbone of SPIDA is research and testing. SPIDA members believe that round and flat-oval duct is the most efficient way to move air in an HVAC system. This is not only due to low static-pressure losses, but also because of negligible leakage rates, strength and overall aesthetics. The testing that SPIDA carries out ensures that the data and research is available to back up these benefits.

One of the most recent projects completed by SPIDA’s technical committee was the flat-oval testing, where deflections of flat-oval duct were tested and correlated with duct pressure, flat span and gauge. 

SPIDA is always looking for suggestions on what the next research project should be — no matter how small or large of an undertaking it may be. 

The use of flat-oval ducts is advantageous in applications where space limitations do not allow the installation of round ductwork. Flat-oval ducts experience lower pressure losses at a given flow rate when compared with a rectangular duct of the same cross-sectional area. Due to their design, rectangular and flat-oval ducts are susceptible to excessive deflections when exposed to substantial positive or negative static pressures. This is amplified when large, flat spans are used on either one. 

Current recommendations related to flat-oval duct reinforcement are available in the Sheet Metal and Air-Conditioning Contractors’ National Association’s HVAC construction manual for metal and flexible ductwork. These standards are based on data obtained for rectangular ducts. The standard only specifies one gauge for each particular major dimension. The goal of SPIDA’s flat-oval study is to develop reinforcement tables for flat-oval ducts, correlating the deflection to variables, such as gauge, flat span and internal pressures, positive and negative. The reinforcing tables produced in the study will provide guidance to engineers and designers with regard to requirements of reinforcement for specific applications.


Test report No. 12-572 of 2013 includes raw deflection data for 12-foot flat-oval sections, including gauges 18 through 26, as well as flat spans of 6 inches to 63 inches. The maximum deflections were reported for a pressure range of negative 6 inches water gauge to 10 inches water gauge. 

Tennessee Tech University studied the results of the SPIDA test report from Texas A&M University to correlate duct deflection as a function of duct gauge, flat span and internal static-gauge pressure — positive and negative — for unreinforced flat-oval spiral ducts. 

In addition to the original scope, the study was extended to analyze raw deflection data for externally and internally reinforced flat-oval spiral ducts having minor dimensions of 16 inches. Only those cases for which sufficient data was available were analyzed. These additional cases included:

  • Ducts with T-25 transverse connectors spaced 12 feet apart, positive and negative pressure
  • Ducts with trapeze external reinforcement spaced 6 feet apart, positive pressure
  • Ducts with attached reinforcement spaced 3 feet apart, positive pressure
  • Ducts with internal tie rods spaced 6 feet apart, positive pressure.
  • A power curve-fit equation was used to correlate the data. The resultant equations were used to create flat-oval deflection tables for each of the reinforcement types tested, as well as unreinforced.

The tables have been made available to high-level SPIDA members. 

There is additional testing and financing that would be required to obtain the data needed to create the equation and tables for other flat-oval gauge/reinforcement combinations. Tennessee Tech proposed to develop these additional reinforcement tables for spiral flat-oval ducts similar to those created from the analysis of data from test report No. 12-572 from Texas A&M and those currently available for rectangular ducts in the SMACNA HVAC duct construction standards manual.
They would also develop a nonlinear finite element model of flat-oval duct in “Ansys,” a computer-aided engineering software including finite element simulation for structural analysis, to predict duct deformations at various pressures for the specific cases described in this proposal. SPIDA is currently looking for partners and funding to extend the study and to include the finite element analysis. 

SPIDA is pleased with the results of the original scope of the flat-oval study, which was based on reinforced flat-oval duct. During the study, it was apparent that the scope of research could be extensively expanded to include several configurations of internal and external reinforcement. SPIDA is currently in communication with SMACNA, with regard to having the tables from this study included in the next printing of the SMACNA duct-construction manual. The flat-oval duct reinforcement tables are currently available at no cost to high-level SPIDA members, and at a nominal fee for other levels of SPIDA membership, as well as the engineering community.