Double Wall Ductwork Specification

Constructed of a perforated inner shell surrounded by a layer of insulation and covered by a solid outer shell.

Double wall ductwork specification.

Insulation will be flexible or semi rigid fiberglass with a maximum thermal conductivity of 0 27 btu hr ft 2 f inch. Standard acoustical double wall is for noise control. Information required for duct construction 1. Gasketed up to 36 flanged or spiralmate by ductmate industries connections are also available.

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. 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 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. A comprehensive duct layout indicating sizes design airflows pressure class and routing of the duct system.

Our double wall duct and fittings also control radiated noise better than similar sizes and shapes of externally insulated sheet metal duct. This requirement is applicable to 20 gauge or less in thickness and 3 w g. In addition to the above any variable air volume system duct of 1 w g. Standard connections are slip fit with couplings.

Langdon fabricates double wall ductwork with an inner perforated metal liner and fittings with an inner solid metal liner. And up b all transverse joint and longitudinal seams 3 w g. 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. Duct wall penetrations 4 w g.

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. 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. Double wall fittings are manufactured on our state of the art fabrication equipment. Double wall insulated spiral is available with solid or perforated liners.

Langdon provides stainless steel and aluminum double wall duct and fittings for a wide range of environments including hospitals laboratories food and pharmaceutical plants. When a perforated inner liner is specified a retaining fabric must be wrapped between the perforated inner and the glass fiber insulation. C transverse joints 2 w g. Construction class that is upstream of the vav boxes shall also meet seal class c.