A house acts much like a chimney and the process is referred to as the “chimney affect”. Cold air will “infiltrate” (pull in) at the lowest level of the home and then that air will be warmed up and rise in pressure through the building, where it will “exfiltrate” (push out) through leaks at the highest level of the home. Exfiltration is nearly impossible to identify under natural conditions as the heat that is leaking out is difficult to feel.
These locations leak constantly regardless of if the wind is blowing, and it happens 24 hours a day during the heating season. To find these leaks, a blower door (part of an energy assessment) is utilized to create a vacuum on the homes interior, causing all the leaks to pull in and at an exaggerated rate allowing us to find them, quantify their effect on the home, and seal them in the most effective manner. A favorite analogy is, if you could pick a house up and flip it over, then fill it with water, wherever the water would leak out is the same place air is leaking through it now.
Examples of Infiltration:
Examples of Exfiltration: