I noticed in the new B149.1-10 Gas Code that Table 5.2 has a note at the bottom,
QuoteNOTE: The outdoor air intake referred to in this Table is the ducting that goes from the outside of the structure and terminates into the return air plenum before the appliance, sometimes referred to as a fresh-air intake.
I'm thinking this NOTE should be eliminated as it contradicts the Gas Code Clause 8.3.1,
QuoteClause 8.3.1 - Except as specified in Clauses 8.3.3 and 8.3.4, a duct shall be used to provide the outside air supply required by 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 least the same cross-sectional area as the free area of the air-supply inlet opening to which it connects; and
(d) terminate within 1 ft (300 mm) above, and within 2 ft (600 mm) horizontally from, the burner level of the appliance having the largest input.
I've always been taught that an outdoor air supply should not terminate inside a return air duct.