An airtightness test is a whole building test that measures how easy it is for air to leak through a building's enclosure or “skin.” In residential construction air leakage tests are often referred to as blower door tests, because these tests are most commonly conducted using a piece of equipment called a blower door.  A large fan or “blower” is used to extract air from or supply air to the building. For larger buildings, that is, with a floor area of over about 929m2,  this test usually requires numerous co-ordinated blower doors running at the same time. In all cases, a building must be prepared for testing beforehand by blocking intentional openings such as HVAC intake and exhaust grills, kitchen and bathroom exhaust fans, relief dampers, etc. The test equipment measures the airflow (how much air is moved into or out of the building) and the corresponding pressure difference acting across the building enclosure.

The trends are clear: the building industry is going to be required to meet airtightness targets, either because they are added to building codes or energy programs or because owners are looking for better buildings – buildings with less energy consumption, more comfort, better indoor air quality, and lower risk of moisture damage. One of the ways architects can use airtightness tests is to prove to the owner and code officials that the contractors and the designer together have delivered a good, airtight building enclosure. It provides quantitative verification that the methods used were successful, much like crushing a concrete cylinder shows that the required concrete strength was achieved.