The required combustion air openings for a vented wall furnace may be omitted if a permanent cased opening into adjacent areas is provided. The minimum combined volume required to eliminate the need of combustion air openings is _ ___ cubic feet.

The required combustion air openings for a vented wall furnace may be omitted if a permanent cased opening into adjacent areas is provided. The minimum combined volume required to eliminate the need of combustion air openings is _ ___ cubic feet.