Air infiltration is the uncontrolled movement of outside air into a building through gaps, cracks, and penetrations in the envelope, contributing to energy loss, comfort problems like drafts, and potentially introducing moisture that could condense within wall or attic cavities.
This uncontrolled entry differs fundamentally from intentional, controlled ventilation, which is deliberately designed and managed through specific vents or mechanical systems, whereas infiltration occurs through unintended gaps never specifically designed as air pathways.
Blower door testing provides a standardized, quantifiable measurement of a home’s total air infiltration rate, giving builders and energy auditors an objective number to compare against code requirements or track improvement after air sealing work is completed.
What Contributes to Air Infiltration?
- Gaps around windows, doors, and other penetrations
- Unsealed rim joist areas
- Electrical, plumbing, and duct penetrations
- Attic hatches and recessed lighting fixtures
Why Is Air Infiltration Important?
Excessive air infiltration contributes significantly to energy loss and comfort problems, and it can also introduce moisture into wall or attic cavities where it might condense and cause hidden mold or rot, making air sealing a genuinely important factor in both energy performance and building durability. This dual impact has driven increasing building code attention to infiltration limits alongside traditional insulation requirements.
Because air infiltration often occurs through small, individually modest gaps that add up to a significant cumulative effect, systematic air sealing addressing many small penetrations throughout a home typically produces better results than focusing exclusively on one or two obvious large gaps. This systematic approach to sealing tends to outperform focusing on just one or two obvious problem areas.
Air Infiltration vs. Air Leakage
These terms are largely interchangeable, both describing uncontrolled air movement through a building envelope, with air infiltration sometimes specifically emphasizing air entering the structure while air leakage can describe movement in either direction.