Q:

# What is the difference between CFM and SCFM?

A:

CFM, or cubic feet per minute, denotes the unit of compressed airflow for air conditioning units. SCFM stands for standard cubic feet per minute, a measurement that takes into account standard conditions. Cubic feet per minute indicates how much air flows through air conditioning as the machinery pushes air through ducts of a building. An air conditioner produces roughly 400 cubic feet per minute per ton of cooling capacity.

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Standard cubic feet per minute determines the weight of compressed air at 14.696 pounds per square inch, 60 degrees Fahrenheit and zero percent relative humidity. These are the conditions that occur at sea level. Even with so-called standard conditions, these measurements differ between the United States, Europe and other countries that use international units.

Cubic feet per minute indicates how much air is moved through the fan of an air conditioner, assuming the fan speed remains constant. Under theoretical conditions, if the fan remains constant, the same volume of air moves through the system from the time the fan starts until it stops.

A third designation, ACFM, or actual cubic feet per minute, takes into account pressure, humidity and temperature as air expands and compresses. Air contracts when the temperature drops and expands as the temperature rises. ACFM also takes into account changes in volume of air as conditions change.

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