Fan Calculations – Measure Airflow with CFM

With one formula, you can find what fan is right for your home. This is the formula for fan CFM: Cubic feet per minute, more commonly known as CFM is calculated by the following formula: air speed (feet per minute) X area (square feet)=CFM. Not everyone is going to take a look at CFM, but for those who do it is a helpful tool. In simpler words than that of the formula, it is the amount of air a fan moves.

The amount of air depends on some other factors as well, such as the diameter and shape of the blades, speed at which the blades turn (revolutions per minute or rpm), horsepower (hp) of the motor, and overall fan design. These combined factors establish the air moving capacity of a fan. Fan capacity is measured in terms of the cubic feet, and again, this is how CFM (cubic feet per minute is determined.)

CFM and RPM are the two most important things to look for in a fan, so that you are guaranteed correct and effective operation. If you only know the RPM, and not the CFM, or vice versa, you should feel confident in your fan purchase. As long as you know one of the calculations, you are ensured of a well-working fan. However, if you are not satisfied with these calculations, this is not the only criteria one can use for evaluating fan performance.

One of the main qualifications, second to rpm and CFM measurement is noise level or decibel rating, followed by the next qualification of vibration. Look for fan noise levels rated in sones or decibels. Check these if the CFM or RPM still leave you unsettled about your fan choice.

A standard measurement of airflow indicates how many cubic feet of air passes by a stationary point in one minute. The higher the number, the more air is being forced through the system. The volumetric flow rate of a liquid or gas in cubic feet per minute equals the CFM, and one CFM equals approximately 2 liters per second.

Fan manufacturers base their measurements on a standard measurement with clean, dry air at a density of 0.075 pounds mass per cubic foot, barometric pressure at sea level of 29.92 inches of mercury, and a temperature of 70°F. These standard measurements are used to determine SCFM: Standard Cubic Feet Per Minute.

With the use of CFM and RPM, you can make a more educated choice when choosing your home ceiling, exhaust, or table fan, and know what you are getting!