ACH50arvo

ACH50arvo refers to the air-change-rate at 50 pascals, a standard metric of building airtightness. The term is commonly used in Finnish-language documentation, where arvo means value; thus ACH50arvo is the measured ACH50 value for a given building.

Measurement is performed with a blower door test, which pressurizes or depressurizes the building to 50 Pa and measures the airflow required to maintain that pressure. The test yields Q50 in m3/h, and ACH50 is calculated as Q50 divided by the building volume in m3. Standards such as ISO 9972, EN 13829, and, in the United States, ASTM E779 govern the procedure.

Interpretation: A lower ACH50 indicates a tighter envelope and lower uncontrolled infiltration. Typical values vary: modern, well-sealed new homes often report 0.6–1.5 ACH50, while older or retrofit buildings may range from 2–5 ACH50; values above 7 ACH50 usually indicate substantial leakage. ACH50 is used in energy performance calculations, building codes, and certification programs to assess efficiency and ventilation needs.

Improvement: To reduce ACH50, builders seal obvious leaks around penetrations, doors and windows, seal ductwork, and improve the overall air barrier. After remediation, a follow-up blower door test confirms the improvement. Proper ventilation must be provided to maintain indoor air quality, typically via mechanical ventilation with heat recovery in airtight buildings.