Clause 8.3.1
(8.3.1) Except as specified in Clause 8.3.3 and 8.3.4, a duct shall be used to provide the outside air supply required Clauses 8.2.1 and 8.2.4. The duct shall
(a) be of either metal or a material meeting the Class I requirements of CAN/ULC-S110;
(b) communicate directly with the outdoors;
(c) be of at the least same cross-sectional area as the free area of air supply inlet opening to which it connects; and
(d) terminate within 1 ft above, and within 2 ft horizontally from, the burner level of the appliance having the largest input.
(a) be of either metal or a material meeting the Class I requirements of CAN/ULC-S110;
(b) communicate directly with the outdoors;
(c) be of at the least same cross-sectional area as the free area of air supply inlet opening to which it connects; and
(d) terminate within 1 ft above, and within 2 ft horizontally from, the burner level of the appliance having the largest input.