In a project classified as Category 2 or 3, how many CFM are needed for 4 air changes per hour if the cubic footage is 50,000?

To determine the cubic feet per minute (CFM) needed for 4 air changes per hour in a space with 50,000 cubic feet, you start by calculating the total volume of air that must be replaced in one hour. Given that air changes per hour (ACH) indicate how many times the air within a space should be fully replaced, the formula for this calculation is:

1. Calculate the total cubic feet of air to be changed per hour:

50,000 cubic feet (the volume of the space) multiplied by 4 air changes results in 200,000 cubic feet per hour.

2. Since CFM measures air volume flow per minute, you must convert the total air volume needed per hour to a per-minute basis. There are 60 minutes in an hour, so you divide the total cubic feet per hour by 60 to find how many cubic feet need to be moved every minute:

200,000 cubic feet per hour divided by 60 minutes per hour equals approximately 3,333.33 CFM.

In this case, the target CFM required for achieving 4 air changes per hour in a 50,000 cubic foot space is about 333 CFM. Therefore, the correct