# Air Filter Classification Explained: From Pre-Filters to HEPA & ULPA

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> Last updated: 2026-09-23 19:10:17
Indoor air quality relies heavily on air filters, which act as the core defense against particulate pollution. From residential HVAC systems and office ventilation to hospital operating rooms and semiconductor cleanrooms, different filter classes serve very different purposes.

Based on internationally recognized standards, this guide explains air filter classifications, filtration principles, testing methods, and real-world applications—helping you choose the right "air protection network" for your needs.

## Understanding Air Filter Classifications: International Standards

![Understanding Air Filter Classifications: International Standards](/storage/posts/2512/191766141850796421.jpeg)

Globally, air filter performance is mainly defined by two standards:
- EN 1822 (Europe) – Focuses on efficiency at the Most Penetrating Particle Size (MPPS)
- ASHRAE 52.2 (USA) – Uses MERV (Minimum Efficiency Reporting Value) ratings

These standards divide air filters into four main categories according to their filtration capability and intended application.

| Filter Class | EN 1822 (EU) | ASHRAE 52.2 (US) | Primary Filtration Capability |
| --- | --- | --- | --- |
| Pre-filter | G1–G4 | – | ≥5 μm particles (hair, dust, fibers) |
| Medium filter | F5–F9 | – | ≥1 μm particles (pollen, smoke, bacteria) |
| HEPA filter | H10–H14 | MERV 17–18 | 0.3 μm particles (PM2.5, viruses, aerosols) |
| ULPA filter | U15–U17 | – | – |

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