603.5 Flexible Air Ducts. Flexible air ducts shall comply

with UL 181, and shall be installed in accordance with the manufacturer’s installation instructions and SMACNA HVAC Duct Construction Standards – Metal and Flexible. Flexible air duct installations shall comply with the following: (1) Ducts shall be installed using the minimum required

length to make the connection.

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.

(1) Ducts shall be installed using the minimum required

length to make the connection. (2) Horizontal duct runs shall be supported at not more than

4 feet (1219 mm) intervals.

(2) Horizontal duct runs shall be supported at not more than

4 feet (1219 mm) intervals. (3) Vertical risers shall be supported at not more than 6 feet

(1829 mm) intervals.

(3) Vertical risers shall be supported at not more than 6 feet

(1829 mm) intervals. (4) Sag between support hangers shall not exceed ¹ ⁄2 inch

(12.7 mm) per foot (305 mm) of support spacing.

(4) Sag between support hangers shall not exceed ¹ ⁄2 inch

(12.7 mm) per foot (305 mm) of support spacing. (5) Supports shall be rigid and shall be not less than 1 ¹ ⁄2 inches

(38 mm) wide at point of contact with the duct surface.

(5) Supports shall be rigid and shall be not less than 1 ¹ ⁄2 inches

(38 mm) wide at point of contact with the duct surface. (6) Duct bends shall be not less than one duct diameter bend

radius.

(6) Duct bends shall be not less than one duct diameter bend

radius. (7) Screws shall not penetrate the inner liner of non-metallic

flexible ducts unless permitted in accordance with the

(7) Screws shall not penetrate the inner liner of non-metallic

flexible ducts unless permitted in accordance with the manufacturer’s installation instructions. (8) Fittings for attaching non-metallic ducts shall be beaded

and have a collar length of not less than 2 inches (51 mm)

122 2019 CALIFORNIA MECHANICAL CODE

DUCT SYSTEMS

(9) 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

TABLE 603.10 CLOSURE MARKINGS

(9) 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. (10)Duct outer vapor barriers shall be secured using two

wraps of approved tape. A mechanical fastener shall be

(10)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. (11) Flexible air ducts shall not penetrate a fire-resistance rated assembly or construction.

(11) Flexible air ducts shall not penetrate a fire-resistance rated assembly or construction. (12)The temperature of the air to be conveyed in a flexible air

duct shall not exceed 250°F (121°C).

(12)The temperature of the air to be conveyed in a flexible air

duct shall not exceed 250°F (121°C). (13)Flexible Air ducts shall be sealed in accordance with Sec tion 603.10.

(13)Flexible Air ducts shall be sealed in accordance with Sec tion 603.10.