A gas fired furnace with an input rating 140,000 Btu is located in a confined space. Combustion air is provided by 2 openings communicationing directly to the outdoors. What is the minimum free area of each opening in square inches ?

A gas fired furnace with an input rating 140,000 Btu is located in a confined space. Combustion air is provided by 2 openings communicationing directly to the outdoors. What is the minimum free area of each opening in square inches ?