For this test, the Blower Door is used to pressurize the house to 25 Pascals and the Duct Blaster pressurizes the ductwork to the same pressure. All duct leakage is measured to the outside, or unconditioned space, and represents heating or cooling energy lost. This test will let you know what percentage of air is being lost in your home to the outside. Don't pay to heat or cool the outside!
Fun Fact: Home Improvement's Tool Time with Tim Allen once featured the Minneapolis Blower Door™. This episode aired in 1997.