The leakage of air from a building is measured through a blower fan door system which, along with other UK-calibrated equipment, gives the air permeability of the building. The test involves connecting the blower fan door to a suitable door in the building envelope and pressurising the building over a range of pressure differences. The fan speed is increased in steps up to a maximum and then decreased in steps...”
Air leakage is the uncontrolled flow of air through gaps and cracks in the building envelope. This is not to be confused with ventilation, which is the controlled flow of air into and out of the building through purpose-built ventilators...”