603.0 Installation of Ducts
Metal ducts shall be installed with not less than 4 inches (102 mm) separation from earth. Ducts shall be installed in a building with clearances that will retain the full thickness of fireproofing on structural members.
Factory-made air ducts shall be installed with not less than 4 inches (102 mm) of separation from earth, except where installed as a liner inside of concrete, tile, or metal pipe and shall be protected from physical damage.
The temperature of the air to be conveyed in a duct shall not exceed 250°F (121°C). Flexible air connectors shall not be permitted.
Flexible air duct installations shall comply with the following:
- Ducts shall be installed using the minimum required length to make the connection.
- Horizontal duct runs shall be supported at not more than 4 feet (1219 mm) intervals.
- Vertical risers shall be supported at not more than 6 feet (1829 mm) intervals.
- Sag between support hangers shall not exceed 1/2 inch (12.7 mm) per foot (305 mm) of support spacing.
- Supports shall be rigid and shall be not less than 11/2 inches (38 mm) wide at point of contact with the duct surface.
- Duct bends shall be not less than one duct diameter bend radius.
- Screws shall not penetrate the inner liner of non-metallic flexible ducts unless permitted in accordance with the manufacturer's installation instructions.
- Fittings for attaching non-metallic ducts shall be beaded and have a collar length of not less than 2 inches (51 mm) for attaching the duct.
Exception: A bead shall not be required where metal worm-gear clamps are used or where attaching metallic ducts using screws in accordance with the manufacturer's installation instructions.
- Duct inner liner shall be installed at not less than 1 inch (25.4 mm) on the collar and past the bead prior to the application of the tape and mechanical fastener. Where mastic is used instead of tape, the mastic shall be applied in accordance the mastic manufacturer's instructions.
- Duct outer vapor barriers shall be secured using two wraps of approved tape. A mechanical fastener shall be permitted to be used in place of, or in combination with, the tape.
- Flexible air ducts shall not penetrate a fire-resistance-rated assembly or construction.
- The temperature of the air to be conveyed in a flexible air duct shall not exceed 250°F (121°C).
- Flexible Air ducts shall be sealed in accordance with Section 603.10.
Factory-made air ducts that are in accordance with UL 181 shall be supported in accordance with the manufacturer's installation instructions. Other ducts shall comply with SMACNA HVAC Duct Construction Standards — Metal and Flexible.
Joints and seams and reinforcements for factory-made air ducts and plenums shall comply with the conditions of prior approval in accordance with the installation instructions that shall accompany the product. Closure systems for sealing factory made air ducts and plenums shall be listed and labeled in accordance with UL 181A or UL 181B, and marked in accordance with Table 603.10.
TABLE 603.10 CLOSURE MARKINGS
|TYPE OF DUCTWORK||STANDARD||TYPE OF CLOSURE SYSTEM||MARKING|
|Rigid Metallic or Rigid Fiberglass||UL 181A||Pressure Sensitive Tape||181A-P|
|Rigid Metallic or Rigid Fiberglass||UL 181A||Mastic Tape||181A-M|
|Rigid Metallic or Rigid Fiberglass||UL 181A||Heat Sensitive Tape||181A—H|
|Flexible Air Ducts||UL 181B||Pressure Sensitive Tape*||181B-FX*|
|Flexible Air Ducts||UL 181B||Mastic*||181B-M*|
* Mechanical fasteners shall be used in conjunction with a listed pressure sensitive tape or mastic in accordance with UL 181. Nonmetallic mechanical fasteners shall be listed and labeled in accordance with UL 181B and labeled "181B-C".
Lmax = CLP0.65
|Lmax||=||maximum permitted leakage, (ft3/min)/100 square feet [0.0001 (m3/s)/m2] duct surface area.|
|CL||=||six, duct leakage class, (ft3/min)/100 square feet [0.0001 (m3/s)/m2] duct surface area at 1 inch water column (0.2 kPa).|
|P||=||test pressure, which shall be equal to the design duct pressure class rating, inch water column (kPa).|