Weatherization experts, those friendly folks that insulate and air seal homes, have developed several tools to aid them in diagnosing air leakages in a home. A blower door test is just such a diagnostic tool; this specific test artificially creates a vacuum between your home and the outside, which causes a pressure difference between the two areas. To begin the test, the weatherization technician will first close all exterior doors and windows in the home and will then set up a large fan in the front door of the house. This fan faces outside and is sealed on all sides to the edge of the door with small hoses running both outside and inside to measure the air pressure. When the fan has created a pressure difference of 50-pascals in cubic feet per minute (CFM) the airflow through the fan is then measured. This number can be translated into a ‘level of leakage,’ which tells a weatherization expert how much air sealing needs to be done. The harder it is to pull air through the fan the harder it is to pull extra air through exterior cracks or holes, which means the house is at a lower level of leakage.