Air infiltration, or leakage, occurs when outside air enters a building or home uncontrollably through cracks and openings. Properly air sealed homes can have significantly reduce heating and cooling costs, improved building durability, and will allow for a healthier indoor environment.

Using a home's air leakage for ventilation is not wise because it can't be controlled. Too much air may enter the house during cold or windy weather. The opposite can happen when it's warmer and less windy. Air leakage can also produce problems with moisture control. Allergies can worsen when moldy and dusty air leaks into a house through attics, foundations or crawlspaces.

Both new and old homes should have air leakage reduced as much as possible to control the problems associated with it.

More information from the U.S. Department of Energy can be found here.