Outside air for horizontal combustion is defined as an opening size of 1 square inch per 2000 BTU, not less than 3 inches.

Outside air for horizontal combustion is defined as an opening size of 1 square inch per 2000 BTU, not less than 3 inches.

• A. 1 square inch for every 2000 BTU, not less than 3 inch
• B. 1 square inch for every 4000 BTU
• C. 2 square inches per 2000 BTU
• D. 1 square inch per 1000 BTU

Answer: (A)

Outside air for horizontal combustion is sized by the appliance’s input: you need 1 square inch of outside air opening for every 2,000 Btu/h, with a minimum of 3 square inches. This ensures adequate air supply for proper combustion, even when the space is tight or has limited airflow. The statement matches this rule exactly, making it the correct choice. For example, a 40,000 Btu/h appliance requires 20 square inches of opening (40,000 ÷ 2,000 = 20), which is above the minimum. The other options use the wrong basis (per 4,000 or 1,000 Btu/h) or omit the minimum, so they don’t comply.

Outside air for horizontal combustion is sized by the appliance’s input: you need 1 square inch of outside air opening for every 2,000 Btu/h, with a minimum of 3 square inches. This ensures adequate air supply for proper combustion, even when the space is tight or has limited airflow. The statement matches this rule exactly, making it the correct choice. For example, a 40,000 Btu/h appliance requires 20 square inches of opening (40,000 ÷ 2,000 = 20), which is above the minimum. The other options use the wrong basis (per 4,000 or 1,000 Btu/h) or omit the minimum, so they don’t comply.