Fan Calculations: Measure Airflow with CFM
With a formula, you can find the right fan for your home. Here is the formula for the fan’s CFM: Cubic Feet Per Minute, more commonly known as CFM, is calculated using the following formula: Air Velocity (Feet Per Minute) X Area (Sqft) = CFM. Not everyone is going to take a look at CFM, but for those who do it is a useful tool. In simpler words than the formula, it is the amount of air moved by a fan.
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 power (hp) of the motor, and the overall design of the fan. These factors combined establish the air movement 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 RPM, and not 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 assess fan performance.
One of the primary ratings, after rpm and CFM measurement, is the noise level or decibel rating, followed by the next vibration rating. Look up fan noise levels rated in sones or decibels. Check them off if the CFM or RPM still leaves you unsure about your fan choice.
A standard measurement 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 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 of mass 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.
Using CFM and RPM, you can make a more informed decision when choosing the ceiling, exhaust, or table fan for your home, and know what you’re getting!