What is the minimum free area required for each opening when providing combustion air in an unconfined space?

The minimum free area required for each opening when providing combustion air in an unconfined space is based on the rate of input of the appliances being used, expressed in BTUs per hour. Correctly identifying this requirement is crucial for ensuring adequate combustion air supply, which is essential for optimal combustion efficiency and safety.

In this case, the correct answer is based on established standards that dictate that 1 square inch of free area is necessary for every 4,000 BTUs per hour of appliance input. This guideline helps in determining how much combustion air is needed to suffice the requirements of gas-burning appliances in unconfined spaces. The rationale behind this figure ensures that there is sufficient airflow to support the combustion process without risking the production of harmful byproducts such as carbon monoxide, which can occur if combustion is starved of the necessary oxygen.

The chosen figure (1 sq in per 4,000 Btu/h) is most applicable to typical residential and commercial applications, providing a reasonable balance between safety and efficiency. It reflects a comprehensive understanding of airflow dynamics in unconfined spaces, which is vital to the safe operation of gas appliances.