SMACNA
HVAC Duct Construction Standards
Metal and Flexible
Third Edition - 2005
The information below is only an excerpt of the original document as a reference for those looking to purchase Gripnail® products. The full text can be found at www.smacna.org
7.4 - Installation Standards For Rectangular Ducts using Flexible Liner
7.5 - Commentary
7.5.1 - Liner Fastener Commentary
Fig. 7-11
Fig 7-12
7.4
INSTALLATION STANDARDS FOR RECTANGULAR DUCTS USING FLEXIBLE LINER
S2.6
Ducts with interior widths of 8" (203mm) or less do not require mechanical fasteners in addition to adhesive.
S2.7
Except as noted in S2.6, mechanical fasteners shall be located with respect to interior dimensions and regardless of airflow direction as in the accompanying table and in Figure 7-11.
| Velocity |
Transversely Around Perimeter |
Longitudinally |
|
2500 fpm (12.7mps) and less
|
At 4" (102mm) from longitudinal liner edges, at 6" (152mm) from folder corner and at intervals not exceeding 12" (305mm) |
At 3" (76mm) from transverse joints and at intervals not exceeding 18" (457mm) |
| 2501 fpm (12.7mps) to 6000 fpm (30.5mps) |
At 4" (102mm) from longitudinal liner edges, at 6" (152mm) from folder corners and at intervals not exceeding 6" (152mm) |
At 3" (76mm) from transverse joints and at intervals not exceeding 16" (406mm) |
S2.11
Liners shall also be installed with mechanical fastening devices that:
- Are spaced in accordance with Figure 7-11,
- When installed, are as corrosion resistant as G60 coated galvanized steel,
- Will not adversely affect the fire resistance classification of liner and adhesives,
- Do not damage the liner when applied as recommended by the manufacturer,
- Do not cause leakage in the duct,
- Do not project more than nominally into the airstream
- Will indefinitely sustain a 50lb. (22.7kg) tensile dead load test perpendicular to the duct wall
- Are the correct length specified for the liner thickness used, and
- Are installed with pins perpendicular to the duct wall.
7.5
COMMENTARY
These standards assume that the designer of a duct system has:
- Examined the liner reference texts listed in the front of this document (which can be found in the full version of this document here);
- Clearly designated on the contract drawings the amount of ductwork to receive lining;
- Specified the type of liner, the thickness and density of liner and the type of liner, adhesive to be used;
- Determined that the specified liner materials have the acoustical, friction loss, and other performance characteristics required for the application; and
- Provided for condensation control where the interruption of the liner would cause a problem.
Typically, duct liner is of flexible fibrous glass material of 1" (25mm) thickness and 1.5lbs per cubic feet (24kg/m3) density. It is primarily used for its sound absorption characteristics, although it may have some thermal resistance value. Molded round liner is available. Metal wall inner lining is available for all conventional duct shapes; typically it is of 22 gauge (0.85mm) galvanized steel with 3/32" (2.4mm) diameter holes on 3/16" (4.8mm) or 1/4" (6.4mm) centers. The double-wall style of lined duct is used where increased resistance to damage is desired or where erosion of the liner surface might occur.
Standard felxible liner is normally shop-installed. Minor damage to the liner surface may occur in transportation and handling.
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