From G4 to HEPA: Understanding Air Filter Efficiency Grades in One Article

Coarse, Medium, High, Ultra-High – Who Should Guard Your Air?

Abstract

Air filters serve as the "first line of defense" for indoor air quality, precision equipment protection, and personnel health. However, professional terms like G4, F7, H13, U15, and international standards such as EN 779, ASHRAE, and ISO 16890 can be overwhelming. This article systematically explains air filter efficiency grading—from the most basic G4 coarse filters to the highest-grade ULPA ultra-high efficiency filters. Through comparison tables, application scenario analysis, and selection guides, it helps you quickly understand the core value of different filter grades, enabling you to choose the optimal filtration solution for your project or equipment.

1. Why Do We Need Filter Grading?

1.1 Different Scenarios Demand Different Cleanliness Levels

The air cleanliness requirements for a home air purifier, an operating room, and a wafer fab are vastly different:

If all scenarios used HEPA filters, costs would be prohibitively high and fan energy consumption enormous. If only coarse filters were used, precision equipment would quickly become contaminated. A scientific filter grading system allows users to select the "right fit" product, balancing protection effectiveness with economic efficiency.

1.2 The Golden Rule of Multi-Stage Filtration

Modern air handling systems generally adopt a multi-stage filtration strategy:

Outdoor Air → Coarse Filter (G4) → Medium Filter (F7-F9) → HEPA/ULPA Filter (H13-U17) → Clean Air

• Coarse Filter: Intercepts large particles (pollen, dust, insects), protects downstream filters
• Medium Filter: Captures fine particles (PM2.5, bacteria), handles the main filtration load
• HEPA/ULPA Filter: Removes submicron particles (virus carriers, nano dust), achieves ultimate cleanliness

This "cascading protection" strategy both extends the life of expensive high-efficiency filters and reduces overall system energy consumption.

2. Major International Filter Grading Standards

Before diving into each filter grade, it's essential to understand the main international standards:

2.1 Comparison of the Three Major Standard Systems

2.2 The Revolutionary Changes in ISO 16890

ISO 16890 replaced EN 779 as the mainstream international standard, with core changes including:

• From "Average Efficiency" to "Minimum Efficiency": Through anti-static treatment, it measures more conservative real-world performance
• From "Single Particle Size" to "Full Particle Size Coverage": Directly reflects capture capability for PM1, PM2.5, and PM10
• From "Vague Grading" to "Transparent Efficiency": "ePM1 65%" is more informative than "F8"

2.3 Standard Cross-Reference Table

3. Coarse Filters: The System's "First Line of Defense"

3.1 Definition and Standards

Coarse filters generally refer to products of grades G1-G4 (EN 779), MERV 1-8 (ASHRAE), or ePM10 < 70% (ISO 16890). They primarily capture large particles >5-10μm.

3.2 Typical Applications

3.3 Core Characteristics and Selection Tips

Common Misconception: "Coarse filters aren't important; just buy the cheapest."
Reality: A quality coarse filter effectively protects expensive downstream filters, reducing overall TCO by 20-30%.

4. Medium Filters: Handling the "Primary Filtration Load"

4.1 Definition and Standards

Medium filters cover grades F5-F9 (EN 779), MERV 9-16 (ASHRAE), or ePM2.5 40% - ePM1 >80% (ISO 16890). They serve as the workhorse for HVAC systems and cleanroom pre-filtration, handling the majority of particulate load.

4.2 Typical Applications

4.3 Core Characteristics and Selection Tips

Common Misconception: "Higher efficiency medium filters are always better."
Reality: Excessive efficiency increases pressure drop and may raise fan energy consumption. Choose the "right-fit" efficiency based on actual cleanliness requirements.

5. HEPA/Sub-HEPA Filters: The Core Barrier for Cleanrooms

5.1 Definition and Standards

HEPA (High-Efficiency Particulate Air) filters generally refer to grades H10-H14, with filtration efficiency for 0.3μm particles ranging from ≥85% (H10) to ≥99.995% (H14). Sub-HEPA filters fall between F9 and HEPA, such as E10-E12.

Primary standards: EN 1822 (Europe), ISO 29463 (International), IEST-RP-CC001 (US).

5.2 Typical Applications

5.3 Core Characteristics and Selection Tips

Key Parameters:

• MPPS (Most Penetrating Particle Size): The particle size filters capture least efficiently, typically between 0.1-0.3μm
• Scanning Leak Test: HEPA filters must undergo in-situ scanning leak testing after installation to verify integrity

Common Misconception: "All HEPA filters are the same; buy the cheapest."
Reality: HEPA filter manufacturing processes (separator/mini-pleat), seal design, and leak testing directly impact actual performance. Poor-quality HEPA may have bypass leakage, rendering efficiency claims meaningless.

6. ULPA Filters: The Pinnacle of Ultimate Cleanliness

6.1 Definition and Standards

ULPA (Ultra-Low Penetration Air) filters refer to grades U15-U17, with filtration efficiency for 0.1-0.2μm particles ranging from ≥99.9995% (U15) to ≥99.999995% (U17). They are used in applications demanding the highest cleanliness levels.

6.2 Typical Applications

6.3 Core Characteristics

Media: Ultra-fine glass fiber or PTFE membrane

Configuration: Mini-pleat design maximizes filtration area

Testing: MPPS testing with significantly higher efficiency requirements than HEPA

Cost: Several times higher than HEPA; used only in most demanding applications

Common Misconception: "HEPA is sufficient; ULPA isn't necessary."
Reality: For advanced process chips (7nm and below), a single 0.1μm particle can ruin a chip; HEPA's 99.97% efficiency is insufficient.

7. Special Function Filters

7.1 Activated Carbon/Chemical Filters

Used to remove gaseous pollutants (VOCs, formaldehyde, SO₂, NOx, odors, etc.). Often combined with particulate filters to form composite filtration systems.

Typical Applications:

• Data centers: Remove corrosive gases
• Hospitals: Remove odors and VOCs
• Commercial buildings: Fresh air system formaldehyde removal
• Chemical plants: Toxic gas protection

Selection Considerations:

• Adsorption capacity: Determines service life
• Pressure drop: Affects system energy consumption
• Targeting: Different pollutants require different adsorbents

7.2 Electrostatic Filters

Use electrostatic principles to charge particles before they are captured on collector plates. Advantages include very low airflow resistance; disadvantages include potential ozone generation and efficiency decline as charge dissipates.

7.3 Antimicrobial/Antiviral Filters

Add antimicrobial agents (silver ions, copper ions, etc.) to media or use special treatments to inhibit microbial growth. Typically combined with HEPA filters.

8. Multi-Stage Filtration Configuration Strategies

8.1 Typical Configuration Solutions

8.2 Configuration Principles

• Progressive Efficiency: Gradually increase from coarse to high efficiency
• Dust-Holding Match: Pre-filters should have sufficient dust-holding capacity to protect downstream filters
• Pressure Drop Balance: Total pressure drop should not exceed fan capabilities
• Maintenance Accessibility: Each stage should have independent pressure monitoring and replacement access

8.3 Common Configuration Mistakes

9. Selection Decision Guide

9.1 Decision Framework

• Step 1: Define Protection Objectives
  Protect personnel health? → Focus on PM2.5, bacteria, viruses
  Protect equipment/processes? → Focus on particle size, corrosive gases
  Protect the environment? → Focus on emission standards
• Step 2: Determine Target Efficiency Grade
  Based on industry standards (e.g., GMP, ISO 14644) or application requirements
• Step 3: Assess Environmental Conditions
  Dust concentration, humidity, temperature, presence of corrosive gases
• Step 4: Balance Efficiency and Energy Consumption
  Choose the lowest pressure drop product that meets efficiency requirements
• Step 5: Calculate Lifecycle Cost
  Initial purchase + operating energy + replacement consumables + maintenance labor

9.2 Balancing Efficiency and Energy Consumption

Taking a 100,000 m³/h AHU as an example:

Conclusion: Excessive filtration efficiency can impose significant energy costs; selection requires comprehensive consideration.

9.3 Procurement Checklist

• Does the supplier provide test reports from accredited laboratories (ISO 16890 or EN 1822)?
• Are key performance data provided (initial pressure drop, dust-holding capacity, efficiency curves)?
• Does the product meet required flame retardancy ratings (UL94, UL900)?
• Is the configuration suitable for installation space?
• Are pressure monitoring interfaces or optional sensors available?
• Does the supplier offer on-site leak testing (for HEPA filters) services?

10. Future Trends

• Standard Unification: ISO 16890 is replacing EN 779 globally, becoming the international standard
• Intelligent Monitoring: Real-time pressure drop monitoring and predictive maintenance becoming standard
• Green Sustainability: Biodegradable media, low-energy designs gaining attention
• Multifunctional Integration: Combined particulate filtration + chemical adsorption + antimicrobial products
• Nanofiber Technology: Next-generation media offering higher efficiency with lower pressure drop

Frequently Asked Questions

Q1: Which standard is more authoritative, ISO 16890 or EN 779?
A: ISO 16890 is the current international standard; EN 779 was officially withdrawn in 2022. New projects should prioritize ISO 16890 for filter selection.

Q2: Are F7 and MERV 13 equivalent?
A: They roughly correspond, but different standards use different test methods, so actual performance may vary. ISO 16890 test reports provide the most reliable reference.

Q3: Can HEPA filters block viruses?
A: H13/H14 HEPA filters achieve ≥99.95% efficiency for 0.3μm particles. Viruses typically attach to aerosols in the 0.3-1μm range and can be effectively captured.

Q4: Do washable filters actually save money?
A: In dusty environments, washable filters can be reused for 2-3 years, significantly reducing consumable costs. However, proper cleaning methods are essential to avoid media damage.

Q5: How do I know when to replace HEPA filters?
A: Monitor with a differential pressure gauge: replace when pressure drop reaches 2-3 times initial value. For cleanroom applications, periodic integrity testing is also required.

Q6: Why does my filter pressure drop rise rapidly?
A: Possible reasons include high ambient dust concentration or inadequate pre-filtration. Check whether the pre-filter is being replaced in a timely manner.

Q7: Which is better, pleated or bag filters?
A: Pleated filters are more compact, suitable for space-constrained applications; bag filters have larger filtration area and higher dust-holding capacity, ideal for high-dust environments.