Infiltration
is the unintentional or accidential introduction of outside air into a building,
typically through cracks in the building envelope and through use of doors
for passage. Infiltration is sometimes called air leakage.
Infiltration measures
The infiltration rate is the volumetric flow rate of outside air into a building, typically in cubic feet per minute. The air exchange rate is the number of interior volume air changes that occur per hour. The air exchange rate is also known as air changes per hour.Controlling infiltration
Because infiltration is uncontrolled, and admits unconditioned air, it is generally considered undesirable except for ventilation air purposes. Typically, infiltration is minimized to reduce dust, to increase thermal comfort, and to decrease energy consumption. For all buildings, infiltration can be reduced via sealing cracks in a building's envelope, and for new construction or major renovations, by installing continuous air retarders. In buildings where forced ventilation is provided, their HVAC designers typically choose to slightly pressurize the buildings by admiting more outside air than exhausting so that infiltration is drammatically reduced.Energy savings
In typical modern U.S. residences, about one-third of the HVAC energy consumption is due to infiltration. Another third is to ground-contact, and the remainder is to heat losses and gains through windows, walls, and other thermal loads. As such, reducing infiltration can yield significant energy savings, with rapid payback.