(1)
Except as permitted by Sentences (2) to (5) and 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 other noncombustible material.
(2)
Except as permitted by Sentence (3), 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, “Standard Methods of Test for Air Ducts,”
(b)
conform to Article 3.1.5.18. 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 permitted to be of combustible construction, and
(f)
are not used in air duct systems in which the air temperature could be more than 120°C.
(3)
Combustible ducts which are part of a duct system conveying only ventilation air and are contained entirely within a dwelling unit need not comply with the requirements of Sentences (1) and (2).
(4)
Duct sealants shall have a flame-spread rating not more than 25 and a smoke developed classification not more than 50.
(5)
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, “Standard Methods of Test for Air Ducts,”
(b)
be not more than 4 m long,
(c)
be used only in horizontal runs, and
(d)
not penetrate a required fire separation.