6.2.4.2 — Duct Design

(1) Except as provided in Sentences (2) to (4) and in Article 3.6.4.3., all ducts, duct connectors, associated fittings and plenums used in air duct systems shall be constructed of steel, aluminum alloy, copper, clay or similar noncombustible material. (2) Ducts, associated fittings and plenums are permitted to contain combustible material provided they, (a) conform to the appropriate requirements for Class 1 duct materials in CAN/ULC-S110, “Test for Air Ducts”, (b) conform to Article 3.1.5.15. in a building required to be of noncombustible construction or in a building or part of a building permitted to be of encapsulated mass timber construction, (c) conform to Subsection 3.1.9., (d) are used only in horizontal runs in a building required to be of noncombustible construction or in a building or part of a building permitted to be of encapsulated mass timber construction, (e) are not used in vertical runs serving more than 2 storeys in a building required to be of noncombustible construction, and (f) are not used in air duct systems in which the air temperature may exceed 120°C. (3) Duct sealants shall have a flame-spread rating of not more than 25 and a smoke developed classification of not more than 50. (4) Duct connectors that contain combustible materials and that are used between ducts and air outlet units shall, (a) conform to the appropriate requirements for Class 1 air duct materials in CAN/ULC-S110, “Test for Air Ducts”, (b) be limited to 4 m in length, (c) be used only in horizontal runs, and (d) not penetrate required fire separations. (5) Materials in Sentences (1) to (4) installed in a location where they may be subjected to excessive moisture shall have no appreciable loss of strength when wet and shall be corrosion-resistant. (6) All ductwork and fittings shall be constructed and installed in conformance with SMACNA Manuals and ASHRAE Handbooks. (7) All duct materials and fittings shall be, (a) suitable for exposure to the temperature and humidity of the air being conveyed, and (b) resistant to corrosion due to contaminants in the air being conveyed in the duct.