I have recently been getting some experience using a blower door. This is a device that is used to measure the amount of air infiltration in a building. The amount of air changes per hour that occur because of air passing through cracks in the buildings envelope has a big impact on the energy used for heating and cooling. Air leaks generally occur at the seams around windows, doors, and other holes. An R2000 home should have less than 1.5 ACH (air changes per hour) while a passive house sets its standard at 0.6 ACH.
The blower door connects to an exterior door frame of the building and covers the entire opening. It uses a large fan to create a pressure difference of 50 pascals between the interior and the exterior. Once the pressure difference is in place you can check for leaks in the building envelope by using smoke. If you see smoke being drawn through the envelope you mark the area and come back and seal it better after the test.
I recently took part in a blower door test for a passive house. Since 0.6 ACH is so low and hard to achieve the builder had a preliminary blower door test done early in the construction process to identify problem areas while they could still be fixed. Often blower door tests are done at the end of the construction when it is too late to fix problems, and I was impressed with the extra steps being taken to ensure efficiency.
The blower door I used is called the Minneapolis Blower Door and is manufactured by the Energy Conservatory.
Blower door set up on a passive house