What is the formula to calculate air changes per hour (ACH)?

The formula for calculating air changes per hour (ACH) is derived from the relationship between the airflow rate in cubic feet per minute (CFM) and the volume of the room in cubic feet.

To calculate the ACH, you take the airflow rate (CFM), multiply it by 60 to convert it from a per minute rate to a per hour rate since there are 60 minutes in an hour. This gives you the total volume of air supplied in one hour in cubic feet. Then, you divide this value by the volume of the room. This calculation indicates how many times the entire volume of air in the room is replaced with fresh air in one hour.

This approach effectively provides a clear measure of ventilation effectiveness, which is critical in healthcare settings for maintaining indoor air quality and ensuring patient safety.

The other choices do not correctly reflect the relationship needed to calculate ACH, thus making them unsuitable for this purpose.