According to the Code, when the volume of a room does NOT provide adequate combustion air for a gas fired furnace, approximately 1/2 of the required combustion air must be supplied by a vent within the upper ____ ” of the enclosure.

According to the Code, when the volume of a room does NOT provide adequate combustion air for a gas fired furnace, approximately 1/2 of the required combustion air must be supplied by a vent within the upper ____ ” of the enclosure.