I. GENERAL

A. All round supply, return and exhaust ductwork shown on the plans or indicated in the project specification to be insulated shall be SPIROsafe® Double Wall as manufactured by Lindab, Inc (800) 797-7476 or approved equal. The duct system shall consist of fittings that are factory fitted with a sealing gasket and spiral duct which, when installed according to the manufacturer's instructions, will seal the duct joints without the use of duct sealer.

B. The contractor may, at his option, convert any or all double wall rectangular or oval ductwork to double wall round provided that the project space limitations are properly addressed and that the overall system design static pressure not be exceeded.

II. MATERIALS

A. Unless otherwise noted, all duct and fittings shall be G-90 galvanized steel in accordance with ASTM A-653 and A-924.

B. Perforated liner on double wall duct shall consist of 1/8 inch perforations on 1/4 inch staggered centers corresponding to an overall open area of 23%.

C. Fiber glass insulation shall have a maximum conductivity factor (K) of 0.26 BTU-in/hr o ft2 o °F at 75°F mean ambient temperature.

D. Retaining fabric shall be 0.008 inch thick, 15.6 lb/ft3 density with an air permeability rate of 9.2 ft3/ft2 o s.

E. When specified on contract documents, stainless steel type 304 or 316 in accordance with ASTM A-240 shall be provided.

F. Insulation stop shall be closed cell polyethylene foam, 1.7 lb./ft3 in accordance with ASTM E-84, ASTM E-162.

III. CONSTRUCTION

A. Unless otherwise noted, all double wall duct and fittings shall be constructed as shown in the following gauge table:

B. FITTINGS:

1. All double wall fitting ends shall come factory equipped with a double lipped, U-profile, EPDM rubber gasket. Gasket shall be manufactured to gauge and flexibility so as to insure that system will meet the performance criteria set forth in the manufacturer's literature. Gasket shall be classified by an internationally recognized laboratory authority to conform to ASTM E84-91a and NFPA 90A flame spread and smoke developed ratings of 25/50.

2. Double wall duct and fittings shall consist of a perforated or solid inner liner, a 1-inch, 1.50 lb/ft3 (unless otherwise specified) layer of fiberglass insulation and a solid outer pressure shell. When a perforated inner liner is specified, a retaining fabric shall be wrapped between the perforated inner and the fiberglass insulation. This fabric provides fiber tear retention while maintaining acoustical properties. For 1-inch thick insulation, the outer pressure shell diameter shall be 2 inches larger than the inner liner.

3. All double wall duct and fittings shall be furnished with a foam insulation stop. Fitting inner liner shall be flush with the outer shell. Duct inner liner shall be recessed.

4. All fitting ends shall be calibrated to manufacturer's published dimensional tolerance standard.

5. All fitting end outer diameters shall have rolled over edges for added strength and rigidity during installation and shipping.

6. Double wall to single wall transitions shall be provided where insulated duct connects to non-insulated, single wall duct. Transitions reduce the double wall outer shell diameter to the inner shell diameter.

7. When contract documents require divided flow fittings, only full body fittings will be accepted. Double wall saddle taps are unacceptable.

8. The inner liners shall not be fastened together to allow for expansion and contraction.

C. SPIRAL DUCT:

1. Spiral duct shall be calibrated to manufacturer's published dimensional tolerance standard.

2. All spiral duct 12" diameter and larger shall be corrugated for added strength and rigidity. Inner and outer duct shall be of spiral lockseam construction.

3. Spiral seam slippage shall be prevented by means of a flat seam and a mechanically formed indentation evenly spaced along the spiral seam.

IV. PERFORMANCE

A. Duct system performance shall meet SMACNA's Leakage Class 3 requirements at the design static pressure as indicated on the contract documents not to exceed -20 In W.G. or +12 In W.G.

(top)