What Is a Blower Door Test?

A blower door test is a specialised way of measuring how airtight a building is. It shows how much outside air leaks into your home through gaps, cracks, and penetrations.

Why Airtightness Matters

• Energy efficiency — leaky homes lose conditioned air
• Comfort — draughts and cold spots reduced
• Durability — prevents hidden condensation
• Compliance — required for Passive House, increasingly referenced by NCC

How Does It Work?

1. Seal all external doors and windows.
2. A calibrated fan is fitted into a doorway and runs to create a pressure difference of 50 pascals.
3. The fan measures the airflow needed to maintain that pressure.
4. Results are calculated as airtightness in ACH (air changes per hour).
5. Leaks can be located using a smoke pencil or thermal camera while the fan runs.

When Should You Do One?

• Existing homes — to benchmark before upgrades
• During construction — mid-build testing before plasterboard so leaks can still be fixed
• At handover — to confirm airtightness goals have been met

Understanding Results

ACH@50Pa

• 10–20 ACH — typical older Australian home
• 5–10 ACH — modern code-built home
• Below 5 ACH — energy-efficient home
• 0.6 ACH — Passive House standard

Air Permeability (q50 or m³/h·m²)

Leakage per square metre of envelope area. This metric is preferred for larger buildings and makes comparisons across different building sizes more meaningful.

Finding Leaks

• Smoke pencils or fog machines
• Thermal imaging cameras
• Hand-held airflow detectors