How to Properly Calculate CFM’s for Air Ventilation

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Calculating CFM’s is a skill that any contractor who's worth their salt can perform. This technique measures airflow in a room to determine several factors like proper fan sizing and air exchange rates according to safety and construction standards. Different rooms require different CFM's for their specific functions, such as bakeries, bowling alleys, and welding rooms. Homeowners can also learn how to calculate CFM’s with these simple guidelines.

1. Use a cubic feet per minute calculator device.

While this advice may appear counterproductive, it will help you get a 'better feel' for the ideal air velocity in hands-on situations. It's a good idea to use a device that's easy to operate and is Bluetooth compatible so you can record the data for future study.

2. Know how to measure in more ways than one.

Basing your fan calculation from an air balancing hood alone seems like a good idea but is actually off 10% of the air duct system's designed capacity. Most small fans can be installed with this variation, but more accurate measurements are required for larger fans. To overcome this, learn how to measure the CFM via at least two different fan calculator methods. The Plot Plan Airflow and Airflow Traverse strategies are good examples.

3. Learn basic fan calculation formulas. 

This practical math formula goes a long way when you're considering air ventilation improvement in an indoor space:

  • CFM = (fpm * area), where fpm is the feet per minute.
  • To find the cubic feet per minute, substitute the FPM value with the area after the area is squared.

Other details are involved in calculating CFMs, but they all stem from these basics. For more help, try using our CFM calculator tool here, or contact us for help anytime.

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