What is a Blower Door Test?

A blower door test is a diagnostic procedure used to measure the airtightness of a building envelope. It is a critical tool in assessing energy efficiency, identifying air leakage paths, and ensuring compliance with UK Building Regulations (particularly Part L: Conservation of Fuel and Power). The test is commonly used in new builds, retrofits, and residential extensions to validate ventilation strategies and thermal performance.

A blower door test involves mounting a calibrated fan in an exterior doorway, which depressurises or pressurises the building to measure air leakage. The results are quantified as air changes per hour (ACH) at a reference pressure (typically 50 Pascals, written as ACH₅₀). Lower ACH₅₀ values indicate better airtightness.

Explanation:

  1. Purpose:
    • Identifies uncontrolled air leakage, which impacts energy efficiency, indoor air quality, and thermal comfort.
    • Validates compliance with Part L1B (Existing Dwellings) and Part L1A (New Dwellings) of the Building Regulations.
    • Supports Passivhaus certification, where airtightness thresholds are stricter (≤ 0.6 ACH₅₀).
  2. Procedure:
    • A fan is sealed into an external door frame.
    • The building is depressurised to 50 Pa while airflow rates are measured.
    • Infrared thermography or smoke pencils may be used to locate leaks.
  3. Real-World Applications:
    • Retrofits: Detects gaps around windows, loft hatches, or service penetrations.
    • New Builds: Ensures compliance with Approved Document L (2021 edition).
    • Ventilation Design: Informs Mechanical Ventilation with Heat Recovery (MVHR) system sizing.

Synonyms:

  • Airtightness Test (commonly used interchangeably in UK construction).
  • Air Permeability Test (though technically distinct, often conflated in practice).

Related Terms:

  1. Air Permeability – Measured in m³/(h·m²) @ 50 Pa, the air leakage per square metre of building envelope.
  2. ACH₅₀ – Air Changes per Hour at 50 Pascals, the standard metric for airtightness.
  3. Part L (Building Regulations) – Governs energy efficiency requirements in England and Wales.
  4. MVHR (Mechanical Ventilation with Heat Recovery) – A system often required in airtight homes to maintain air quality.
  5. Thermal Bypass – Heat loss caused by air leakage, addressed via blower door testing.
  6. Infiltration Rate – Uncontrolled air leakage into a building.
  7. Passivhaus Standard – A rigorous energy efficiency standard requiring exceptional airtightness.