Double Wall Ductwork Specification

Langdon fabricates double wall ductwork with an inner perforated metal liner and fittings with an inner solid metal liner.

Double wall ductwork specification.

Double wall fittings are manufactured on our state of the art fabrication equipment. Our double wall duct and fittings also control radiated noise better than similar sizes and shapes of externally insulated sheet metal duct. Information required for duct construction 1. Ductwork will be spiral seam construction made from g 90 or better galvanized steel conforming to astm a653 a653m and a924 a924m standards lock forming quality lfq.

The outer shell of double wall construction for 2 or 3 inch insulation thicknesses finish 2 times the insulation thickness larger 4 inch and 6 inch respectively. The types of fittings to be used based on the designer s calculations of fitting losses i e square versus 45 entry taps conical versus straight taps etc. All double wall ductwork and fittings shall be constructed with an outer galvanized wall and a perforated inner galvanized liner. Double wall duct and fittings can reduce radiated noise by 25 db or more compared with fiberglass duct board and by 30 db or more com pared with insulated flexible duct.

In addition to the above any variable air volume system duct of 1 w g. The perforated inner shell has 3 32 diameter holes staggered at 3 16 on center for a clear open area of 23. And up b all transverse joint and longitudinal seams 3 w g. Double wall duct and fittings will consist of a perforated or solid inner liner 1 thick x 1 0 lb ft layer of glass fiber insulation and a solid outer pressure shell.

Langdon provides stainless steel and aluminum double wall duct and fittings for a wide range of environments including hospitals laboratories food and pharmaceutical plants. A comprehensive duct layout indicating sizes design airflows pressure class and routing of the duct system. Gasketed up to 36 flanged or spiralmate by ductmate industries connections are also available. Mylar barrier is available as a barrier between perforated liner and insulation.

Construction class that is upstream of the vav boxes shall also meet seal class c. Insulation will be flexible or semi rigid fiberglass with a maximum thermal conductivity of 0 27 btu hr ft 2 f inch. All double wall fittings are fabricated with stiffening beads on duct sizes 19 wide and larger which have more than 10 square feet of unbraced panel. Standard connections are slip fit with couplings.

Double wall insulated spiral is available with solid or perforated liners. Duct wall penetrations 4 w g. Constructed of a perforated inner shell surrounded by a layer of insulation and covered by a solid outer shell. When a perforated inner liner is specified a retaining fabric must be wrapped between the perforated inner and the glass fiber insulation.