Over the past several years — and several decades — the fabrication and assembly of HVAC ductwork has changed in response to new technology and higher demand from the construction industry. In this post, we'll discuss the differences between today's duct construction and the ducts of the past.
Advances in Modern Duct Construction
One major difference in today's duct construction consists of the transition from slip-on flange to now rolled on flange. At one time, the transverse joint was four, five, or six different processes and techniques. When the four bolt connectors that slide on and roll on came on in Germany years ago, that became the standard around the world. 40 years ago, it would have been hard to believe that one connection would be dominant. Today, that one four bolt connector is the connector of choice worldwide, driving out slip and drive.
Internal reinforcement is another design element that has changed duct construction over the part 25 years. By using two foot coil and use intermediate tie rods, it makes duct work a little bit lighter and easier to construct, therefore affordable as well. The intermediate tie rods act as internal reinforcement versus exterior galvanized angle for reinforcement. In fact, external angle reinforcing in mid panel has largely gone away.
Regional Differences in Duct Construction
As an HVAC profession, if you travel around the country you may sometimes find regional differences in the way that duct is formed and assembled. For example:
- In the Massachusetts area, different drives are used that are rarely seen anywhere else.
- In the Northeast, New England cleat is more often being used than in the Southeast.
- In the Pacific Northwest, you see more two foot coil being used to get away from using galvanized angle, you can use two foot coil and use intermediate tie rods, as opposed to the South.
While industry standards do exist, reducing some of this regional variation, some areas the country are prone to be more "old school" in terms of duct construction. With machinery and software constantly evolving and improving, sometimes the standards aren't implemented right away, and differences in fabrication and construction can lead to these regional differences as well.