Glossary · Testing & air leaks

Air sealing

Also called: draftproofing · draughtproofing · sealing air leaks · caulking and weatherstripping · weatherstripping

Blocking the hidden gaps where air leaks in and out of a house, which cuts drafts, heating and cooling costs, and moisture problems.

What it means

Air sealing uses caulking, spray foam, gaskets, weatherstripping and rigid materials to close leaks, starting with the biggest ones in the attic and basement (see attic bypass and rim joist). A blower door test before and after shows how much leakage was removed. It's normally done before adding insulation, because insulation alone doesn't stop air movement.

Why it matters in an audit

It cuts drafts, heating bills and moisture damage, but a much tighter house may need mechanical ventilation (an HRV or ERV) and a combustion safety test to keep air healthy and appliances venting properly.

Typical numbers

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

What	Value	Source
DOE estimate of savings	10%–20% on heating and cooling bills	energy.gov ↗
Average leakage reduction from retrofits	20%–30% (LBNL analysis of about 134,000 US home tests, 2012)	eta-publications.lbl.gov ↗
Ontario HRSP air sealing rebate	Up to $250 (assessment stream, 2+ upgrades)	homerenovationsavings.ca ↗

In Canada

NRCan warns that stuffing batt insulation into gaps, such as at the basement header, doesn't stop air leaks; use sealants and rigid materials instead.

Sources

Learn more here

Related terms

Air leakage Uncontrolled air moving in and out of a house through cracks and gaps, carrying heat, moisture and outdoor pollutants with it.
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.
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.
HRV (heat recovery ventilator) A ventilation system that swaps stale indoor air for fresh outdoor air while transferring heat from the outgoing air to the incoming air.
Combustion safety test A check that furnaces, boilers, water heaters and stoves burn cleanly and vent their exhaust outside, even with fans running.
Air barrier The continuous layer of materials in walls, ceilings and floors that stops air from leaking through the building envelope.

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