Double Wall Ductwork Specification

Double wall fittings are manufactured on our state of the art fabrication equipment.

Double wall ductwork specification.

Mylar barrier is available as a barrier between perforated liner and insulation. This requirement is applicable to 20 gauge or less in thickness and 3 w g. Construction class that is upstream of the vav boxes shall also meet seal class c. 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.

Insulation will be flexible or semi rigid fiberglass with a maximum thermal conductivity of 0 27 btu hr ft 2 f inch. Constructed of a perforated inner shell surrounded by a layer of insulation and covered by a solid outer shell. In addition to the above any variable air volume system duct of 1 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.

When a perforated inner liner is specified a retaining fabric must be wrapped between the perforated inner and the glass fiber insulation. Langdon fabricates double wall ductwork with an inner perforated metal liner and fittings with an inner solid metal liner. Gasketed up to 36 flanged or spiralmate by ductmate industries connections are also available. A comprehensive duct layout indicating sizes design airflows pressure class and routing of the duct system.

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. All double wall ductwork and fittings shall be constructed with an outer galvanized wall and a perforated inner galvanized liner. Standard connections are slip fit with couplings. 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 perforated inner shell has 3 32 diameter holes staggered at 3 16 on center for a clear open area of 23. Langdon provides stainless steel and aluminum double wall duct and fittings for a wide range of environments including hospitals laboratories food and pharmaceutical plants. 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. Information required for duct construction 1.

C transverse joints 2 w g. And up b all transverse joint and longitudinal seams 3 w g. Our double wall duct and fittings also control radiated noise better than similar sizes and shapes of externally insulated sheet metal duct. Standard acoustical double wall is for noise control.