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CFM (Cubic Feet per Minute)

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CFM by Definition stands for Cubic Feet per Minute. It is the Imperial System for measuring air volume. CFM can also be expressed in the Metric system by Cubic Metre per Minute.
In layman's terms, CFM in reference to an Industrial Exhaust Fan or a Commercial Ceiling Fan, means how much air flow a fan moves and is typically the best way of determining how well the fan will perform the task you are using it for.

An easy way to understand A cubic measurement, no mater what it is, is a volume. Volume of air equals the product of the length, width, and height  (V=l x W x H). These three measurements are measured in feet, and when you multiply "foot" against itself three times, it becomes foot to the third power or foot cubed or cubic feet (CFM). With that known, cubic feet per minute looks like this: ft^3/min, or Cu. Ft per Min.. The velocity at which the volume of air is traveling finishes the equation. This is the most common way of specifying the performance of an exhaust fan or supply fan.

CFM is also key to determining a fan's airflow efficiency. Airflow efficiency is the CFM divided by the watts/amount of energy used to run the fan at its highest speed.

CFM is not the only factor to look at when determing the best fan product for your particular installation. Other factors such as noise level measured in decibels or sones, voltage availability, static pressure which can be caused by inadequate supply air or duct lengths or cross winds, safety guards, environmental conditions such as excessive temperatures, and/or dirty air streams should all play a part in the selection process.

CFM can also be calculated if you know the velocity at which the air flow is traveling through an opening such as a wall louver or an intake shutter. For Example: If you have a velocity of 500 fpm (feet per minute) and the wall opening is 24" x 24" or 2 Ft. x Ft. = 4 sq.ft.. Multiplying the 4 sq.ft. times 500 fpm = 2,000 cfm. This is the amount of air volume traveling through your opening. This can be useful information when trying to determine the number of and size of your fresh air intake shutter or fresh air supply louver needs to be. An inadequate amount of fresh air supply for your exhaust fan means it will have to work harder because of an increase in static pressure. Louvers and Intake Shutters often have a velocity rating, it is important not to exceed that rating. For example, if an intake louver has a velocity rating of 600 fpm (beginning point of water penetration at .01 oz/ft² free area). It is important to consider the free area rating of the louver in consideration. A 48" x 48" louver with an 896 FPM rating and a 56.6% Free Area can only handle 4' x 4' = 16 Sq.Ft. x 896 FPM = 14,336 CFM before water starts entering your building.




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