Air leakage testing, more known as "Blower door", is a very important part of building a low energy or passive house. Usually the special fan is installed on the window or door, which makes 50 pascals under or over pressure in the house. The volume of the air leaking in or out of the the house is then measured. For the passive house, the standard is that air exchange per hour is lower than 0.6 of the whole air in the house. To achieve this result, all the details of the tightening should be carefully planned.
It is very important to test air leakage with both, over pressure and also under pressure, because both could happen in real life and the results can be significantly different.
The photo below show air leakage test of a passive house.