Double Wall Ductwork Specification

Mylar barrier is available as a barrier between perforated liner and insulation.

Double wall ductwork specification.

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. 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. Duct wall penetrations 4 w g. Double wall insulated spiral is available with solid or perforated liners.

All double wall ductwork and fittings shall be constructed with an outer galvanized wall and a perforated inner galvanized liner. Gasketed up to 36 flanged or spiralmate by ductmate industries connections are also available. 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. A comprehensive duct layout indicating sizes design airflows pressure class and routing of the duct system.

This requirement is applicable to 20 gauge or less in thickness and 3 w g. C transverse joints 2 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. Double wall fittings are manufactured on our state of the art fabrication equipment.

Information required for duct construction 1. Insulation will be flexible or semi rigid fiberglass with a maximum thermal conductivity of 0 27 btu hr ft 2 f inch. Our double wall duct and fittings also control radiated noise better than similar sizes and shapes of externally insulated sheet metal duct. Standard connections are slip fit with couplings.

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. Standard acoustical double wall is for noise control. Langdon fabricates double wall ductwork with an inner perforated metal liner and fittings with an inner solid metal 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. When a perforated inner liner is specified a retaining fabric must be wrapped between the perforated inner and the glass fiber insulation. Constructed of a perforated inner shell surrounded by a layer of insulation and covered by a solid outer shell. Construction class that is upstream of the vav boxes shall also meet seal class c.