Do I actually need a blower-door test?

A blower-door test measures how leaky a building's envelope is. A fan mounted in a doorway pulls air out of the house, and instruments measure how hard it has to work to hold a pressure difference. Leakier house, more airflow.

When it's required

• EnerGuide evaluations. The test is part of the standard procedure.
• ENERGY STAR and Net Zero new homes. A measured air-tightness result is mandatory for the label.
• Some code paths and rebate programs that call for a measured air-tightness result.

When it's just useful

• Chasing draughts. Paired with theatrical smoke or a thermal camera, it pinpoints exactly where air is getting in.
• Before drywall on a new build or gut reno. Fixing leaks with the framing exposed costs a fraction of doing it later.
• Verifying a contractor's air-sealing. A number, not a promise.
• Comfort and health. Air leakage drives cold spots, ice damming, and moisture problems in wall cavities.

What the number means

Results are usually given as air changes per hour at 50 pascals (ACH50). Lower is tighter. A typical older house might be 5 to 10; a well-built new home is often under 1.5; the tightest builds are under 0.6. The right target depends on the building and its ventilation strategy. A very tight house needs mechanical ventilation.

Next step

See blower-door testing, or the energy advisory overview.