What is required for combustion air opening size for each opening based on BTU?

For determining the required size of combustion air openings in residential buildings, the appropriate standard is that there should be 1 square inch of opening for every 1,000 BTU of input rating for appliances that utilize combustion air from a confined space. This standard ensures that there is sufficient air available for the combustion process, which is critical for the safe and efficient operation of gas-fired appliances.

Insufficient combustion air can lead to incomplete combustion, resulting in reduced efficiency and potential safety hazards, such as the production of harmful carbon monoxide. By adhering to the guideline of 1 square inch per 1,000 BTU, inspectors can help ensure that installations meet safety standards and operate effectively.

The other options provided do not align with this established requirement, as they suggest different ratios that could lead to inadequate combustion air supply.