A gas-fired water heater with an input of 75,000 Btu/hr is being installed in a confined space. The room has no indoor combustion air openings. The installer plans to use two permanent outdoor air openings, one high and one low, communicating directly with the outdoors. What is the minimum free area required for EACH of these two openings?

• 18.75 square inches.
• 37.5 square inches.
• 1 square inch per 2,000 Btu/h of input.
• 1 square inch per 1,000 Btu/h of input.