We believe that a well informed customer will always have a more gratifying experience. So in that regard, here is the 10 minute ‘expert’ course in airflow. What we won’t discuss for now are the human engineering aspects. Thermal comfort is a complex science.

What is CFM?

You see the numbers everywhere, what does it mean? CFM stands for cubic foot per minute. This term is used as a measurement of airflow rate for ventilation systems. The cubic foot refers to a cube of air 1 foot x 1 foot x 1 foot. CFM represents a volume flow rate, since we measure how many cubic feet are flowing by per minute.

Air is really, really light.

It takes 13.5 cubic feet (101 gallons) of air to weigh 1 pound. For a 2,000 square foot house, that means all the air in that house weighs 1,185 pounds – not much. Warming or cooling air is “low calorie”. To warm all that air in your house up from 50 degrees F to 70 degrees F takes about 5,688 BTU’s. The smallest house furnace puts out 40,000 BTU’s per hour. So how come it takes so long to heat up the house on a cold morning? (hint: you’re not just warming the air) An unsealed door jamb, leaking 50 CFM, would over the course of 24 hours, leak out 72,000 cubic feet of air – not “low calorie.”