For combustion air openings used by fuel-burning appliances, the corrosion-resistant screen must have a minimum opening not less than what?

• A. 1/2 Inch
• B. 1/4 Inch
• C. 3/16 Inch
• D. 1/8 Inch

Answer: (B)

The principle at work is ensuring enough combustion air reaches fuel-burning appliances while keeping pests and debris out. The corrosion-resistant screen on combustion air openings must have openings that are not smaller than 1/4 inch. If the openings were smaller, airflow could be restricted, leading to improper combustion or backdraft conditions. So 1/4 inch is the minimum size that guarantees sufficient air supply; larger openings meet the requirement but the key point is that the opening cannot be smaller than 1/4 inch.