One way to test a specific intersection in the structure for air infiltration while the house is under pressure during the blower door test is to use an anemometer. Here, for example, when the rafter fills the collar beam, a very small penetration rate has been read. Based on the speed of air leaking through the building’s envelope versus building volume, experts can determine the air flow ratio. This provides a lot of information about how well your home skin works. Each authentication type requires a constant maximum flow rate in order for the house to be considered healthy. Basically, all windows and doors are closed. One entrance has a blower door as shown here. The base fan sends air to and from the house depending on the type of test being performed.