Understanding the Air Filter Spectrum
If you have ever stared at an air filter specification sheet wondering whether your facility requires an F7 pocket filter, an H13 HEPA, or a U15 ULPA, you are not alone. The global air filter grading system spans four main tiers—Coarse (G1–G4), Medium (M5–F9), HEPA (H10–H14), and ULPA (U15–U17). Each is engineered to target specific particulate sizes under rigorous test conditions.
Choosing the wrong grade can lead to premature filter failure, excessive energy consumption, or catastrophic contamination in sensitive environments. This guide maps out every grade in detail, explains how standard migrations (like EN 779 to ISO 16890) affect your procurement, and demonstrates how to build a cascading filtration system that optimizes performance and cost.
The Four-Tier Filtration Framework
From basic dust capture to sub-micron cleanroom protection, air filters are categorized into four distinct performance tiers.
Coarse (G1–G4 / ISO ePM10)
Designed to capture particles larger than 10 μm, such as pollen, hair, insects, and heavy outdoor dust. Primarily used as pre-filters in HVAC systems to protect coils and downstream filters.
Medium (M5–F9 / ISO ePM2.5 & ePM1)
Targets atmospheric dust, bacteria carriers, and fine combustion aerosols (1 to 10 μm). The F7 grade is the standard workhorse for modern commercial buildings and LEED ventilation specifications.
HEPA (H10–H14 / ISO 29463)
High-Efficiency Particulate Air filters capturing at least 99.95% (H13) or 99.995% (H14) of particles at the Most Penetrating Particle Size (MPPS, typically 0.1 to 0.3 μm). Vital for pharma and biotech.
ULPA (U15–U17)
Ultra-Low Penetration Air filters offering up to 99.999995% efficiency at 0.12 μm. Reserved for high-tech cleanrooms, semiconductor fabs, and advanced nanotechnology laboratories.
The EN 779 to ISO 16890 Standard Transition
For decades, the European standard EN 779 classified air filters using simple letters and numbers (G1-G4, M5-M6, F7-F9). However, this testing method measured average efficiency against a single synthetic test dust size, which did not accurately reflect real-world ambient pollution.
Introduced globally, the ISO 16890 standard evaluates filter efficiency based on three distinct particulate matter size fractions: ePM1 (0.3–1.0 μm), ePM2.5 (0.3–2.5 μm), and ePM10 (0.3–10 μm). This provides engineers and procurement managers with a much more accurate prediction of how a filter will perform inside an actual air handling unit (AHU).
When buying replacement filters, it is crucial to understand that an old "F7" class is not a single fixed equivalent. Depending on the media design, an F7 filter could map anywhere from ePM1 50% to ePM1 65%. Always request dual-certified test reports to verify you are getting equivalent performance.
Why the Standard Changed:
- Real-world Aerosol Simulation: ISO 16890 tests filters against actual outdoor particle distributions, not just a single laboratory dust.
- Electrostatic Discharge Testing: Filters are tested with and without electrostatic charge, ensuring performance doesn't plummet after a few months of service.
- Global Harmonization: Bridges the gap between the European EN standards and the North American ASHRAE 52.2 (MERV) systems.
Master Air Filter Efficiency Comparison
Use this comprehensive comparison table to cross-reference grades, efficiency ranges, and typical application environments.
| Tier Category | EN 779 / EN 1822 Grade | ISO 16890 Equivalent | Efficiency @ MPPS / Particle Size | Typical Application Fields |
|---|---|---|---|---|
| Coarse | G1 - G2 | ISO Coarse < 50% | Arrestance-based evaluation | Simple ventilation, insect screens, coarse pre-filters |
| Coarse | G3 - G4 | ISO Coarse > 50% / ePM10 50% | Arrestance > 90% (Coarse dust) | AHU first stage, paint booth pre-filters, residential HVAC |
| Medium | M5 - M6 | ePM10 60% - 70% | ePM10 efficiency ≥ 50% | Secondary stage HVAC, food prep areas, paint booths |
| Medium | F7 - F8 | ePM1 50% - 70% / ePM2.5 70% | ePM1 efficiency ≥ 50% - 70% | Commercial office IAQ, pre-filtration for HEPA systems |
| Medium | F9 | ePM1 80% - 85% | ePM1 efficiency ≥ 80% | Data centers, hospitals, gas turbine intake systems |
| HEPA | H10 - H12 | EPA Range (ISO 29463) | 85% to 99.5% @ 0.3 μm | General cleanrooms, food processing, vacuum cleaners |
| HEPA | H13 | HEPA Class (ISO 29463) | ≥ 99.95% @ MPPS (0.1 - 0.3 μm) | GMP Grade B/C cleanrooms, biosafety cabinets, hospitals |
| HEPA | H14 | HEPA Class (ISO 29463) | ≥ 99.995% @ MPPS (0.1 - 0.3 μm) | GMP Grade A aseptic zones, semiconductor fabs (ISO Class 5) |
| ULPA | U15 - U16 | ULPA Class (ISO 29463) | ≥ 99.9995% to 99.99995% @ 0.12 μm | Semiconductor photolithography, wafer processing, nanotech |
| ULPA | U17 | ULPA Class (ISO 29463) | ≥ 99.999995% @ 0.12 μm MPPS | Ultra-clean environments, nuclear exhaust containment |
Application Matrix: Matching Grades to Industries
Every industry has specific particulate standards. Below is how you should match filter grades to meet operational compliance.
Pharmaceutical Cleanrooms
Strict adherence to EU GMP Annex 1 is mandatory. Requires H14 HEPA filters for Grade A aseptic filling zones, and H13 filters for Grade B/C background areas.
Semiconductor Fabs
Sub-micron particles destroy silicon wafers. Lithography bays and mask shops require U15 to U17 ULPA filters combined with chemical molecular filtration.
HVAC & Commercial Buildings
To achieve LEED credits and ensure occupant health, systems should combine a coarse pre-filter with a high-performance medium pocket or V-bank filter.
Data Center Cooling
ASHRAE TC 9.9 guidelines require protection against fine dust and corrosive salts. Multi-stage filtration prevents hardware failure and optimized PUE.
The Cascading Principle: Protecting Your Investment
Installing a standalone high-efficiency filter (like an H14 HEPA) in an air stream without proper pre-filtration is a critical engineering mistake. The high concentration of larger ambient dust particles will clog the micro-glass or ePTFE membrane of the HEPA filter within weeks, causing pressure drop to spike and airflow to drop.
The Cascading Filtration Strategy distributes the particulate load across multiple stages. Each stage is designed to capture a specific range of particle sizes:
- Stage 1 (Coarse G4): Captures 90% of large dust particles, protecting the fan and cooling coils.
- Stage 2 (Medium F7/F9): Removes fine sub-micron dust and soot, extending the life of the final HEPA filter by 3 to 5 times.
- Stage 3 (HEPA H13/H14): The final barrier, capturing 99.95%+ of viruses, bacteria, and sub-micron particulates.
By allocating 15% of your filter budget to high-quality pre-filters, you can save up to 60% on overall replacement and energy costs over the system's lifetime.
Common Procurement Pitfalls to Avoid
When specifying and purchasing air filters, look out for these four common errors that can compromise performance.
1. H13 vs H14 Confusion
A 0.045% efficiency difference might seem minor, but it represents a tenfold increase in particle penetration. For GMP Grade A aseptic cleanrooms, using an H13 instead of an H14 will cause regulatory compliance failure.
2. Ignoring MERV-A Suffix
Standard synthetic filters can rely on electrostatic charges to achieve high initial efficiency. Over time, this charge decays in the field. Always specify filters with the "MERV-A" suffix to ensure stable mechanical efficiency.
3. Incorrect Test Aerosols
HEPA filters can be tested using different aerosol agents like DEHS, PAO, or DOP. Ensure the testing agent used by your filter manufacturer matches the downstream particle counters and validation protocols of your facility.
4. Buying "F7 Equivalents"
Under the ISO 16890 transition, some suppliers sell low-performance filters under old "F7-equivalent" labels. Always demand the exact ePM1 or ePM2.5 rating percentage to ensure you are receiving the correct filtration capacity.
Why Partner with KWS Purification?
Founded in 2011 in the beautiful coastal city of Xiamen, Xiamen KWS Purification Technology Co., Ltd. is a high-tech enterprise integrating R&D, manufacturing, sales, and technical service. Over the past 14 years, we have built a reputation for delivering reliable, certified air filtration solutions globally.
We operate advanced filter production lines, automatic mixing/filling machines, and state-of-the-art testing equipment. All KWS products undergo strict validation by third-party national authoritative organizations to ensure absolute compliance with global standards.
Our Core Competencies
We focus on high-performance materials and customer-centric customization to solve complex cleanroom and HVAC challenges.
Product R&D & Patents
KWS holds 15 patent certificates for air filter products (obtained from 2023 to 2025) and utilizes advanced ePTFE membrane technology for low pressure drop applications.
Customized Engineering
We provide non-standard custom sizes, specialized framing, and custom efficiency options to match unique air handling unit designs.
Fast Turnaround & Delivery
With optimized supply chains and dedicated production lines, we support short delivery cycles, with fast-track orders completed in 3-7 working days.
Our Scale & Commitment
At KWS, we believe that high-performance air filtration is built on a foundation of technical expertise and humanistic values.
The Humanistic Temperature
We firmly believe that a great company is driven by passion and employee well-being. By fostering a supportive workplace—offering flexible hours, health initiatives, and professional growth opportunities—we have been recognized as a "Best Employer" for three consecutive years. This internal care translates directly into how we serve our clients: with empathy, responsiveness, and a deep commitment to technical excellence.
Ready to Optimize Your Air Filtration System?
Whether you need standard G4 pre-filters, custom-sized F7 pocket filters, or ultra-pure H14 HEPA and U15 ULPA modules, KWS is here to assist. Let our engineering team help you design the perfect cascading system for your facility.