Our old house had a flow of 9377 cfm of cold air moving through it during the blower test.
After the initial whole house tour, he brought out his infrared camera to check for insulation in the walls, floors and ceiling.  The infrared camera measures heat, so areas where heat is present (insulation, wall studs, etc) showed up as lighter areas, while colder, non-insulated areas appeared dark. Along the way, he pointed out problems to me – our crawl space needs to be enclosed so that cold air is not drawn through cracks in the uninsulated floor to the rest of the house; our attic storage areas are inside our thermal envelope and are unnecessarily heated; cellulose insulation, for which discounts are offered through the audit program, cannot be used in areas where the older knob and tube electrical systems are present, as in much of our house. The list went on and on, unfortunately. The highlight of the audit was the blower test. An industrial sized fan, or blower, was placed in a seal in our inner porch door with the outer door open. Tubes were attached through the blower and to a nanometer gauge. When the blower was turned on, we toured the house again, feeling the changes in temperature from the cold air that was being drawn into the house through all the leaks. In some places, we could feel the air blowing with our hands, or see cobwebs moving from the air flow. It was pretty dramatic. Our old house had a flow of 9377 cfm of cold air moving through it during the blower test. That’s pretty leaky! By the end of the 10 minute blower test, the temperature in the house had dropped 3 degrees, from a comfortable 68 to a slightly chilly 65.