Glossary · Testing & air leaks

Air leakage

Also called: air infiltration · infiltration · exfiltration · air leaks · uncontrolled air leakage · air leakage rate

Uncontrolled air moving in and out of a house through cracks and gaps, carrying heat, moisture and outdoor pollutants with it.

What it means

Air leaks in through some gaps in the building envelope (infiltration) and out through others (exfiltration), pushed by wind, the stack effect and exhaust fans. Common leak spots include attic hatches, plumbing and wiring holes, recessed lights, the rim joist (header), window and door frames, outlets and fireplace dampers. It's measured with a blower door test.

Why it matters in an audit

Sealing air leaks typically cuts heating and cooling bills by 10%–20% (DOE), and air moving through walls and attics carries moisture that can cause condensation, mold and, in cold climates, ice dams.

Typical numbers

Reference values with their sources. Your auditor’s report gives the figure for your own house.

What	Value	Source
Moisture carried by air vs. diffusion	One small air leak can carry about 100 times more moisture than diffusion through materials	natural-resources.canada.ca ↗
Typical savings from sealing leaks (DOE estimate)	10%–20% of heating and cooling bills	energy.gov ↗

Sources

Learn more here

The blower door test, step by step →

Related terms

Air sealing Blocking the hidden gaps where air leaks in and out of a house, which cuts drafts, heating and cooling costs, and moisture problems.
Blower door test A test that uses a powerful, calibrated fan in an outside doorway to pull air out of the house and measure how leaky it is.
Stack effect Warm indoor air rises and escapes near the top of a house, pulling cold outside air in near the bottom; it's strongest on cold days.
Attic bypass A hidden opening from the living space into the attic, around chimneys, plumbing stacks, wiring, pot lights or wall tops, that leaks warm air.
Rim joist (header) The band of framing on top of the foundation wall around the edge of the floor; it's prone to air leaks and often poorly insulated.
Air barrier The continuous layer of materials in walls, ceilings and floors that stops air from leaking through the building envelope.
Building envelope Everything that separates inside from outside — foundation, walls, windows, doors and roof — and controls heat, air and moisture flow.

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