Filter Rating

A filter rating describes an air filter's ability to capture airborne particles of various sizes. The current standard is ISO 16890, which classifies filters by their efficiency in capturing particles of specific sizes: ePM1 (very fine particles below 1 micron), ePM2.5 (fine particles below 2.5 microns), and ePM10 (coarse particles below 10 microns). Higher percentages indicate better filtration.

Choosing the right filter rating is a balance between air quality and energy consumption. A higher-rated filter captures more particles, improving indoor air quality for allergy sufferers and sensitive individuals. However, denser filters also create more airflow resistance, which increases fan energy consumption and can reduce ventilation capacity if the system is not designed for high-efficiency filters.

For residential supply air, a minimum of ePM2.5 65% (formerly F7) is recommended in Finnish conditions to effectively capture pollen, fine dust, and combustion particles. Allergy sufferers may benefit from even higher-rated filters such as ePM1 55%. Exhaust air filters typically use a coarser rating (ePM10 or G4) since their primary purpose is to protect the heat recovery cell from dust.

Filters should be replaced one to two times per year, or more frequently in dusty environments or during high pollen seasons. A clogged filter dramatically reduces ventilation airflow and increases energy consumption. Check your air handling unit's manual for the correct filter size and recommended replacement schedule for your specific system.