602.5 Nonmetallic Ducts — 2025 California Mechanical Code
California Mechanical Code (Title 24, Part 4) · 2025 edition · updated 2026-09-25 · California
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Italicized text is a California amendment to the model code, as printed in the official publication.
Cite as: 2025 California Mechanical Code (Title 24, Part 4) § 602.5 · Effective January 1, 2026 · Official source: Building Standards Commission
Nonmetallic ducts shall comply with Section 602.5.1, Section 602.5.2, Section 602.5.3, Section 602.5.4, or Section 602.5.5.
602.5.1 Phenolic. Phenolic duct, plenum, or fitting material shall comply with UL 181. Ducts, plenums, or fittings of phenolic shall be constructed in accordance with SMACNA Phenolic Duct Construction Standards or the conditions of its listing.
602.5.2 Gypsum. Where gypsum products are exposed in ducts or plenums, the air temperature shall be restricted to a range from 50°F (10°C) to 125°F (52°C), and moisture content shall be controlled so that the material is not adversely affected. All gypsum products shall have a mold or mildew resistant surface. For the purpose of this section, gypsum products shall not be exposed in supply ducts.
602.5.3 Air Dispersion Systems. Air dispersion systems shall be listed and labeled in accordance with UL
602.5.4 Fibrous Glass Duct. Fibrous glass ducts, plenums, or fittings shall be constructed in accordance with SMACNA Fibrous Glass Duct Construction Stan dards or NAIMA Fibrous Glass Duct Construction Stan dards.
602.5.5 Other Materials. Flexible and rigid ducts, plenums, or fittings for use in heating, ventilation, and air conditioning systems of other nonmetallic materials listed and labeled to UL 181 shall be permitted.
Exception: Plastic ducts shall comply with Section 603.5.
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