What is infiltration as it pertains to energy?

Air leakage is sometimes called infiltration, which is the unintentional or accidental

introduction of outside air into a building, typically through cracks in the building envelope

and through use of doors for passage. In the summer, infiltration can bring humid outdoor

air into the building. Whenever there is infiltration, there is corresponding exfiltration

elsewhere in the building. In the winter, this can result in warm, moist indoor air moving into

cold envelope cavities. In either case, condensation can occur in the structure, resulting in

mold or rot. Infiltration is caused by wind, stack effect, and mechanical equipment in the

building. Wind creates a positive pressure on the windward face and negative pressure on the non-windward (leeward) facing walls, which pulls the air out of the building. Wind causes infiltration on one side of a building and exfiltration on the other. Wind effects can vary by surrounding terrain, shrubs, and trees.