How Do You Use a CFM Calculator?

To use a CFM (cubic feet per minute) calculator to determine airflow needs for a room, know variables such as the volume of the room and the number of times the air changes per hour from the fan/ventilation system and apply them to a formula. CFM is an engineering calculation used to find the heating needs of a room.

When installing home ventilation systems, such as fans, it is necessary to know the air change for each room in the home. Air change is defined as the number of times air flows into and leaves a room in 1 hour. The formula for CFM is CFM = room volume x number of air changes per hour / 60 minutes. To use a fan CFM calculator:

  1. Find the volume of the room
  2. Measure the room’s length, width and height and record the measurement, such as L = 10 feet, W = 8 feet and H = 8 feet. Multiply these numbers to find the room volume of 640 cubic feet.

  3. Determine the number of air changes per hour for a specific room type
  4. Go to the tables of air changes per hour found at Contracting Business and choose the type of room, such as a bathroom, that requires between six and seven air changes per hour. Use an average number, such as seven and a half air changes per 60 minutes.

  5. Find an online CFM calculator
  6. Use the calculator provided by the CSGNetwork site and enter the values for length, width, height and number of air changes into the given fields. Click on the “Calculate” button to find the CFM of 80. Use the given formula to check that this answer is correct.