Fan Calculations – Measure Airflow with CFM
With a formula, you can find the right fan for your home. Here is the formula for fan CFM: Cubic feet per minute, more commonly known as CFM, is calculated using the following formula: Air Velocity (feet per minute) X Area (square feet) = CFM. Not everyone is going to take a look at CFM, but for those who do, it’s a useful tool. In simpler words than those of the formula, it is the amount of air that a fan moves.
The amount of air also depends on other factors, such as the diameter and shape of the blades, the speed at which the blades rotate (revolutions per minute or rpm), the horsepower (hp) of the motor, and the overall design of the fan. These factors combined establish the air moving capacity of a fan. Fan capacity is measured in terms of 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 to ensure proper and effective operation. If you only know the RPM, and not the CFM, or vice versa, you should be confident in your fan purchase. As long as you know one of the calculations, you are guaranteed a well-functioning fan. However, if you are not satisfied with these calculations, this is not the only criteria that can be used to evaluate the performance of the fan.
One of the main ratings, after the RPM and CFM measurement, is the noise level or decibel rating, followed by the next vibration rating. Look up noise levels for fans rated in sones or decibels. Check them off if the CFM or RPM still leaves you unsure about your choice of fan.
A standard measure of airflow indicates how many cubic feet of air pass a stationary point in one minute. The higher the number, the more air is forced through the system. The volumetric flow rate of a liquid or gas in cubic feet per minute is equal to the CFM, and one CFM is approximately equal to 2 liters per second.
Fan manufacturers base their measurements on a standard measurement using clean, dry air at a density of 0.075 mass pounds per cubic foot, a sea level barometric pressure 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 informed decision when choosing the right ceiling, exhaust or table fan for your home, and know what you’re getting!