When using horizontal ducts to introduce outdoor air into an unconfined space, what is the minimum size of the openings required?

The correct answer is based on guidelines for ensuring adequate air supply when using horizontal ducts to introduce outdoor air into an unconfined space. The specification of 1 square inch per 2,000 Btu/h is derived from established industry standards that aim to provide sufficient ventilation and air quality for occupants.

When calculating the opening size, it's important to consider the heat load of the space being conditioned. This ratio helps ensure that enough outdoor air enters to meet the ventilation needs corresponding to the amount of heating or cooling required. If the openings were smaller than this ratio, the system might not effectively manage indoor air quality or comfort levels, as insufficient outdoor air could lead to stale and unhealthy conditions.

In contrast to other options, a larger opening size (higher ratio) would inadequately restrict airflow for spaces with high Btu/h loads and could lead to the system being less efficient in maintaining temperature and humidity levels. Thus, the requirement of 1 square inch per 2,000 Btu/h is a balanced approach to promote efficiency and comfort in such scenarios.