What rough opening is required if the air supply opening is 50 square inches using a grill rated at 75% free area?

To determine the rough opening required for an air supply opening of 50 square inches with a grill that has a free area of 75%, it’s important to understand the relationship between the total area required and the free area of the grill.

The free area is the portion of the grill that actually allows airflow. In this case, if the grill is rated at 75% free area, it means that only 75% of the grill’s total area will contribute to effective airflow. To find out the total area of the grill needed to achieve a specific airflow requirement, you can use the formula:

Total area required = Air supply requirement / Free area percentage.

In this scenario, the air supply requirement is 50 square inches. The grill has a free area percentage of 75%, or 0.75 in decimal form. Therefore, we will set up the equation:

Total area required = 50 square inches / 0.75 = 66.67 square inches.

When rounded, this results in a rough opening requirement of approximately 66.6 square inches, making that the correct answer. This means that to achieve the desired airflow through the grill, the rough opening must be sufficiently large to compensate for the limitations imposed by the grill's