For example, Lindab Inc., Stamford, Conn., introduced at the AHR Expo in Atlanta this year a new double wall spiral connector that is intended to save installation time and produce a better seal.
The new connector fills several needs. The standard means of connecting double wall duct using an inner and outer slip fit connection was cumbersome and time-consuming, and didn't always yield the best of results. Adding to the difficulty were the serrated or scalloped edges on the ends of the perforated inner liner on duct and fittings which made the duct hard to handle cleanly without snagging on insulation or other materials. As a result, some installers routinely request factory installed flanged connections to eliminate the problems associated with the double wall slip fit connections. But they find that the flanging itself adds considerable costs and is also time consuming to align and bolt into place.