Can we provide combustion air to the furnace through the return air ductwork?
Yes, the Dwelling Code, Section 2004.2 allows for “Ducts admitting outdoor air may be connected to the return air side of the heating system.” The Mechanical Specialty Code does not have the same verbiage found in the Dwelling Code, which allows for the connection to the return air duct. All of the requirements found in the Dwelling Code, Section 2004.2, except for the last sentence, can be found in the Mechanical Specialty Code, Section 706.1.1. As an alternate to the requirements found in Section 706, Section 707 of the Mechanical Specialty Code allows the use of a “mechanical forced-air system” to be used to provide combustion air through the buildings mechanical ventilation system.
