The early to mid-1990s was a very difficult time for the industry due to patent litigation initially brought against The Lockformer Company, which at the time was a division of Met-Coil. In March 1991, Lockformer was found guilty of “willful” infringement, throwing the industry into uncertain waters. Eventually, every CAD/CAM company that marketed hardware and software to the HVAC industry and every contractor who had purchased some would be ensnared – none were excluded – eventually eliciting SMACNA’s assistance, to no avail.  

But there were positive things too. In 1995 SMACNA released their Duct Construction Standards (DCS) that for the first time recognized both TDC and TDF as new rectangular construction methods. They tested and rated them giving both a new designation: T-25/A (TDC) and T-25/B (TDF) respectively bringing an end to the industry’s engineering community’s confusion over usage.