Now, let’s get some perspective on what a cubic foot and CFM represent:

• It takes about13.5 cubic feet of air to weigh one pound. A 2,000 square foot house will contain 16,000 cubic feet of air. The weight of all that air is only 1,185 pounds.
• 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?
• 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”