Classification of Air Filters – Filter Ratings
What Classification of Air Filters – Filter Ratings
Air filters are classified based on various factors, including their efficiency in capturing particles, their application, and the method of filtration. The two primary classifications for air filters are based on their efficiency
- MERV Rating:
- Description: Minimum Efficiency Reporting Value (MERV) is a standard that rates the effectiveness of air filters.
- Range: MERV ratings typically range from 1 to 20, with higher values indicating better filtration efficiency.
- Application: Used to categorize filters based on their ability to capture particles of different sizes.
- This can refer to similar levels of standards： EN 779:2012, ISO 16890, and its MEVA
- HEPA Filters:
- Description: High-Efficiency Particulate Air (HEPA) filters are extremely efficient in capturing very small particles.
- Efficiency: HEPA filters can capture particles as small as 0.3 micrometers with high efficiency.
- Application: Commonly used in environments where high levels of air cleanliness are required, such as hospitals, laboratories, and cleanrooms.
- This can refer to similar levels of standards： EN1822-1:2009, ISO 29463
Minimum Efficiency Reporting Value (MERV) – ASHRAE Standard 52.2
The MERV rating system was indeed established by the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE). ASHRAE Standard 52.2, specifically outlines the testing method for determining the performance of general ventilation air-cleaning devices, including air filters, in terms of their removal efficiency by particle size. MERV represents the overall efficiency of an air filter across a range of particle sizes, not just at its lowest performing level. The rating takes into account the filter’s performance in capturing particles ranging from 0.3 to 10 micrometers. It provides a single numerical value that summarizes the filter’s effectiveness across this range.
What is Minimum Efficiency Reporting Value (MERV)
- Developed by the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE).
- MERV ratings range from 1 to 20, with higher values indicating better filtration efficiency.
- MERV focuses on the ability of filters to capture particles in the 0.3 to 10-micrometer< size range.
- Filters with higher MERV ratings are more effective at trapping smaller particles.
MERV is the standard rating system for filters defined in an ASHRAE standard (52.2), which specifies the conditions under which the testing must be done and the performance required to meet each MERV level. Higher-MERV filters remove more particles from your air. They also remove smaller particles. A standard fiberglass one-inch filter is typically a MERV-2. The high end of the scale is MERV-16.
We already explained PM before, we need to define the three general size ranges of particulate matter (PM).
- PM10 – 10µ= 0.01mm3.0 to 10.0 microns
- PM2.5 – 2.5µ= 0.0025mm1.0 to 3.0 microns
- PM1.0 – 1µ= 0.001mm0.3 to 1.0 micron
According to Mechanical Reps, the MERV rating chart breaks down as follows:
- MERV 13 to 16:
- Effectiveness: Controls airborne bacteria, most tobacco smoke, and pollutants released through sneezing.
- Applications: Suitable for use in general surgery suites, smoking lounges, and commercial buildings with advanced HVAC systems.
- MERV 9 to 12:
- Effectiveness: Controls humidifier dust, lead dust, vehicle emissions, and welding fumes.
- Applications: Appropriate for use in residences with advanced HVAC systems, hospital labs, and commercial buildings.
- MERV 5 to 8:
- Effectiveness: Controls mold spores, hair spray, and dust. MERV 8 filters have 90 percent efficiency on particles that are 3 to 10 micrometers in size.
- Applications: Suitable for use in most commercial buildings, residences, industrial workplaces, and paint booths.
- MERV 1 to 4:
- Effectiveness: Controls larger particles such as sanding dust, spray paint dust, lint, and carpet fibers.
- Applications: Applicable in residences and window air conditioning units.
Comparison Table for Filter effectiveness by MERV rating and particle size
| Minimum% of Particles Trapped | |||
|---|---|---|---|
| MERV Rating | 0.3 to 1.0 micron | 1.0 to 3.0 microns | 3.0 to 10.0 microns |
| MERV-16 | >95% | >95% | >95% |
| MERV-15 | >85% | >90% | >95% |
| MERV-14 | >75% | >90% | >95% |
| MERV-13 | >50% | >85% | >90% |
| MERV-12 | >35% | >80% | >90% |
| MERV-11 | >20% | >65% | >85% |
| MERV-10 | >- | >50% | >80% |
| MERV-9 | >- | >35% | >75% |
| MERV-8 | >- | >20% | >70% |
| MERV-7 | >- | >- | >50% |
| MERV-6 | >- | >- | >35% |
| MERV-5 | >- | >- | >20% |
| MERV-4 | >- | >- | >20% |
| MERV-3 | >- | >- | >20% |
| MERV-2 | >- | >- | >20% |
| MERV-1 | >- | >- | >20% |
But Why MERV 8 Is So Popular in America?
- MERV 8 filters are described as two-inch, pleated filters that have been popular in the U.S. since the 1970s. They are commonly used in American households to eliminate basic pollutants present in most homes and to protect the performance and efficiency of the air-conditioning system.
- MERV 8 air filters are efficient at trapping a majority of indoor particulates. They are particularly beneficial for individuals with asthma and allergies, as well as for preventing long-term respiratory problems by reducing exposure to airborne particles.
- MERV 8 filters are noted for being easily serviced. The recommended replacement period varies by manufacturer but is typically every three to six months or as specified in the product instructions.
What is FPR/MPR?
MERV, FPR, and MPR are different rating systems used to measure and categorize the efficiency of air filters for heating, ventilation, and air conditioning (HVAC) systems. Each system has its scale and criteria for evaluating air filter performance.
- FPR (Filter Performance Rating):
- Developed by The Home Depot for their air filter products.
- FPR ratings range from 4 to 10, with higher values indicating better filter performance.
- FPR takes into account factors like particle size efficiency, arrestance, and dust-holding capacity.
- The FPR scale is designed to provide consumers with an easy-to-understand rating for filter effectiveness.
- MPR (Microparticle Performance Rating):
- Developed by 3M for their Filtrete brand of air filters.
- MPR ratings are based on the filter’s ability to capture particles in the 0.3 to 1.0-micrometer size range.
- MPR ratings range from 300 to 2800, with higher values indicating better performance.
- MPR focuses on capturing smaller microparticles, including allergens and fine dust.
FRP is created by filter manufacturer The Home Depot, Rather than use MERV ratings, The details of their testing are a bit murky, as their website explains it in broad strokes only.They start by saying, “FPR-10 is similar in strength to MERV-20 since they are both the highest rating value.” Some filters on their website have both an FPR and a MERV rating, and at least one with an FPR of 10 is shown as equivalent to either MERV-8 or MERV-13.
As with Home Depot’s Filtration Performance Rating, the Microparticle Performance Rating was developed by 3M company with a financial interest in the sale of filters, the maker of the Filtrete line of filters. the MPR measures the effectiveness of a filter’s capturing only the smallest particles on the MERV scale: 0.3 to 1.0 microns. Their website says, “Your filter’s MPR (Microparticle Performance Rating) indicates its ability to capture tiny particles between 0.3 and 1 micron in size.”
While MERV, FPR, and MPR all aim to provide consumers with information about air filter performance, it’s important to note that they are distinct rating systems. If you’re comparing filters, it’s advisable to refer to the specific rating system mentioned on the product or packaging to ensure accurate assessment and compatibility with your HVAC system.
EN 779:2012 – Particulate Air Filters For General Ventilation
- Scope: Developed by the European Committee for Standardization (CEN), This standard is focused on particulate air filters used for general ventilation applications.
- Objective: It aims to determine the filtration performance of air filters, specifically those designed for general ventilation purposes.
- Parameters: The standard defines a classification system for fine filters (F7 to F9) based on Minimum Efficiency (ME) for 0.4 µm particles. The Minimum Efficiency is determined through tests for initial efficiency, efficiency throughout loading, and discharged efficiency.
- Application: EN779:2012 is applicable to filters used in general ventilation systems, where the primary concern is the removal of airborne particles to maintain indoor air quality.
The three tests used to establish the Minimum Efficiency are:
- Initial Efficiency: This measures the filter’s efficiency when it is first installed and has not yet undergone any loading with particles.
- Efficiency Throughout Loading Procedure: This test assesses how the filter performs as it accumulates particles during the loading procedure. It provides information on the filter’s efficiency as it continues to operate and collect particles over time.
- Discharged Efficiency: This measures the efficiency of the filter when it is at the end of its service life or loading capacity, representing its performance after extended use.
The Minimum Efficiency is then defined as the lowest value obtained from these three tests. This approach ensures that the filter is evaluated not only based on its initial efficiency but also considers its performance under various conditions, including during the loading process and at the end of its lifespan.
The particle size chosen for testing is 0.4 µm, which is within the fine particle range. This is a critical size as it represents particles that are small enough to be suspended in the air for extended periods and can have implications for indoor air quality.
Revised Filter Classifications
Compared to EN779:2002, The revised filter class descriptions of EN779:2012 are:
- G1 – G4: Course Filters
- M5 – M6: Medium Filters
- F7 – F9: Fine Filters
Efficiencies of filters as per EN 779
| Filter Class | Final Pressure Drop(Pa) | Average arrestance (Am) of synthetic dust% | Average efficiency (Em) of 0.4 µm particles(%) | Minimum Efficiency (ME) for 0.4 µm particles(%) |
|---|---|---|---|---|
| G1 | 250 | 50 < Am < 65 | – | – |
| G2 | 250 | 65 < Am < 80 | – | – |
| G3 | 250 | 80 < Am < 90 | – | – |
| G4 | 250 | 90 < Am | – | – |
| M5 | 450 | – | 40 < Em < 60 | – |
| M6 | 450 | – | 60 < Em < 80 | – |
| F7 | 450 | – | 80 < Em < 90 | 35 |
| F8 | 450 | – | 90 < Em < 95 | 55 |
| F9 | 450 | – | 95 < Em | 70 |
The characteristics of atmospheric dust differ significantly from synthetic dust used in EN779 tests, affecting the accuracy of predicting filter performance and service life. Potential issues like media charge loss or particle shedding can impact efficiency. The re-grading of M5 and M6 filters, along with the removal of Minimum Efficiency (ME) test requirements, may impact cleanroom design and pre-filter selection for ISO 14644 environments. Designers must consider these changes during the design phase to ensure appropriate testing and documentation, acknowledging the limitations of synthetic dust tests in predicting real-world performance.
ISO 16890 standard for classifying air filters
EN 779 has been the most widely used method of classifying air filters for over 20 years. But from the beginning of 2017, The new standard ISO 16890 came into force and completely changed the way that filters are tested and categorized.
- Scope:ISO 16890 focuses on particulate air filters used in general ventilation applications. These filters are designed to remove airborne particles to maintain indoor air quality.
- Classification System:The standard introduces a classification system for air filters based on their efficiency in capturing particles of different sizes. The classification is expressed in terms of filter classes, such as ePM1, ePM2.5, and ePM10, indicating the filter’s efficiency for particles with diameters of 1 µm, 2.5 µm, and 10 µm, respectively.
- Particulate Matter (PM) Size Ranges:ISO 16890 addresses the efficiency of air filters for particulate matter in different size ranges, aligning with the global interest in monitoring and reducing exposure to fine particulate matter (PM) for health and environmental reasons.
- Testing Procedure:
The standard prescribes a testing procedure to determine the efficiency of air filters under standardized conditions. The test measures the filter’s performance across specified particle size ranges. - Filter Classes:The filter classes defined in ISO 16890 are based on the Minimum Efficiency Reporting Value (MERV) scale commonly used in North America. However, ISO 16890 is considered a global standard, offering a harmonized approach to filter classification.
- Global Applicability:ISO 16890 is intended to be used globally, providing a standardized method for assessing air filter performance that can be adopted by manufacturers, regulatory bodies, and users worldwide.
ISO 16890 is part of the ongoing effort to standardize methods for evaluating and comparing the performance of air filters, contributing to the improvement of indoor air quality and energy efficiency in ventilation systems.
Revised Filter Classifications
Compared to EN779:2012, the revised filter class descriptions of ISO 16890 replace the ‘G’ AND ‘F’ CLASS, Four new filter groups are introduced under ISO 16890: Coarse, ePM10, ePM2.5, and ePM1.
The ‘e’ prefix simply stands for efficiency. To fall into each category, a filter must be capable of capturing at least 50% of the particulate in that size range. Filters capturing less than 50% of PM10 dust go into the Coarse group.
- ISO ePM1: ePM1 min ≥ 50% ( viruses, nanoparticles, exhaust gasses)
- ISO ePM2,5: ePM2,5 min ≥ 50% ( bacteria, fungal and mold spores, pollen, toner dust)
- ISO ePM10: ePM10 ≥ 50% (pollen, desert dust)
- ISO Coarse: ePM10 ≤ 50% (sand, hair)
What does PM1 mean?
PM1 means all Particulate Matter with a size smaller than 1 micron (a thousandth of a millimeter), and just to be clear:
- 1µ= 0.001mm (=PM1)
- 2.5µ= 0.0025mm (=PM2.5)
- 10µ= 0.01mm (=PM10)
Comparison of MERV, EN 779 and ISO 16890
The new ISO16890 test method shifts the focus on filtration performance to the classes of particulate matter size (PM) and is, therefore, a much more realistic test criterion than the theoretical EN779:2012.
The translation of air filter classes between ISO 16890 and EN779:2012 involves aligning the efficiency classifications of the two standards. While these standards have different approaches and criteria, efforts have been made to provide a correspondence between them for practical purposes. Below is a general mapping of classes between ISO 16890 and EN779:
| EN 779:2012 | EN ISO 16890 – Range of currently measured average separation efficiencies | ||||
|---|---|---|---|---|---|
| Filter Class | ISO Coarse | ISO ePM10 | ISO ePM2,5 | ISO ePM1 | |
| Coarse Filters | G3 | >80% | – | – | – |
| G4 | >90% | – | – | – | |
| Medium Filters | M5 | – | >50 % | – | – |
| M6 | – | >60 % | 50 – 60 % | – | |
| Fine Filters | F7 | – | >85 % | 65 – 80 % | 50 – 65 % |
| F8 | – | >90 % | >80 % | 65 – 80 % | |
| F9 | – | >95 % | >90 % | >80 % | |
The Minimum Efficiency Reporting Value (MERV) and ISO 16890 are two different standards used to measure and categorize the efficiency of air filters, particularly in the context of heating, ventilation, and air conditioning (HVAC) systems. Here’s a comparison between MERV and ISO 16890:
| MERV | ISO 16890 | |
|---|---|---|
| Measurement Methodology | MERV is a standard developed by the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE). It focuses on the efficiency of air filters based on their ability to capture particles in the size range of 0.3 to 10 micrometers. | ISO 16890 is an international standard developed by the International Organization for Standardization (ISO). It provides a broader classification based on the efficiency of filters for three particle size ranges: PM1 (particles smaller than 1 micron), PM2.5 (particles smaller than 2.5 microns), and PM10 (particles smaller than 10 microns). |
| Particle Size Range | MERV primarily considers particles in the 0.3 to 10-micrometer range, with a focus on particles in the submicron size. | ISO 16890 covers a wider particle size range, addressing particles smaller than 1 micron, 2.5 microns, and 10 microns. This reflects a more comprehensive approach to air quality standards. |
| Filter Performance Categories | MERV uses a numerical scale from 1 to 20, with higher values indicating better filtration efficiency. Filters are categorized based on their ability to capture particles at different size ranges. | ISO 16890 introduces filter classes such as ePM1, ePM2.5, and ePM10, indicating the efficiency of the filter for particles in specific size ranges. |
| International Adoption | Primarily used in North America, MERV is widely recognized and adopted in the United States and Canada. | ISO 16890 is an international standard and has gained acceptance in various regions globally. It provides a common framework for air filter efficiency testing and classification. |
EN1822-1:2009 – High-Efficiency Air Filters (EPA, HEPA & ULPA)
- Scope: This standard is focused on high-efficiency air filters, including EPA (Efficiency Particulate Air), HEPA (High-Efficiency Particulate Air), and ULPA (Ultra-Low Penetration Air) filters.
- Objective: It provides a classification system and testing procedures for high-efficiency air filters used in various applications, including cleanrooms, healthcare facilities, and industries where strict air quality control is essential.
- Parameters: The standard classifies filters based on their efficiency for different particle sizes and outlines performance testing methods. It includes testing for particulate removal efficiency and pressure drop across the filter.
- Application: EN1822-1:2009 is applicable to high-efficiency air filters used in critical environments where the control of ultrafine particles is crucial, such as in cleanrooms, laboratories, and healthcare settings.
Revised Filter Classifications
Compared to EN1822-1:1998, The revised filter class descriptions of EN1822-1:2009 are:
- E10 – E12: Efficiency Particulate Air (EPA) Filters
- H13 – H14: High Efficiency Particulate Air (HEPA) Filters
- U15 – U17: Ultra Low Penetration Air (ULPA) Filters
High-Efficiency Filters per EN 1822-1
| Filter Group | Integral Value | Local Value | |||
|---|---|---|---|---|---|
| Filter Class/EN 1822 | Collection Efficiency(%) | Penetration% | Collection Efficiency(%) | Penetration% | |
| EPA | E10 | 85 | 15 | – | – |
| E11 | 95 | 5 | – | – | |
| E12 | 99,5 | 0,5 | – | – | |
| HEPA | H13 | 99,95 | 0,05 | 99,75 | 0,25 |
| H14 | 99,995 | 0,005 | 99,975 | 0,025 | |
| UEPA | U15 | 99,9995 | 0,0005 | 99,9975 | 0,0025 |
| U16 | 99,99995 | 0,00005 | 99,99975 | 0,00025 | |
| U17 | 99,999995 | 0,000005 | 99,9999 | 0,0001 | |
Test per EN 1822-1
Testing is typically conducted using an aerosol probe that can be moved over the entire surface of the filter. This scanning process allows for the measurement of local collection efficiencies at different points on the filter.
Integral Value and Local Value:
The moving aerosol probe, or scanning, results in the measurement of many local collection efficiencies. These local efficiencies can be used to calculate two important values:
- Integral Value: This represents the overall efficiency of the filter across the entire particle size distribution range.
- Local Value: This is associated with leak detection and represents the efficiency at specific areas of the filter. For filters with a specification of H13 and above, meeting the Local Value is crucial to ensure there are no leaks.
Testing Conditions:
Tests are conducted on new filters, and the specified nominal volumetric air flow is used for testing. For filters of U15 grade and above, a particle counter probe designed for this purpose is required for scanning. Additionally, an oil thread test can be utilized on filters of H13 and H14 grade.
Filter testing includes the measurement of the following parameters:
- Pressure Drop at Nominal Air Flow: This measures the resistance the filter presents to the airflow.
- Overall Collection Efficiency at Most Penetrating Particle Size (MPPS): Identifies the filter’s efficiency at the particle size where penetration is most significant.
- Local Collection Efficiencies at MPPS: Provides information on the efficiency at specific locations on the filter.
Requirement for H13 and Above Filters:
Filters with a specification of H13 and above must meet the Local Value to ensure there are no leaks. This emphasizes the importance of maintaining the integrity of high-efficiency filters, especially in critical applications such as cleanrooms.
Overall, the testing procedures outlined in EN 1822 ensure a comprehensive evaluation of high-efficiency air filters, covering aspects such as overall efficiency, leak detection, and pressure drop, essential for applications where strict control of airborne particles is necessary.
ISO 29463 – New test standard for HEPA Filters
EN 1822 provides the basis for the new ISO 29463. ISO 29463 is a standard derived from EN 1822 and is closely related to filter classes commonly used in industrial settings, namely EPA, HEPA, and ULPA. While maintaining these filter designations, ISO 29463 replaces the previous filter classes (E10-E12, H13-H14, U15-U17) with a new set of 13 filter classes, ranging from ISO 15 E to ISO 75 U. This standard builds on EN 1822 and provides a comprehensive classification system for filters, ensuring consistency in terminology and performance specifications across various industries.
The new ISO 29463 does not replace the EN 1822 standard. EN 1822 will continue to be valid!
Comparison of EN 1822 and ISO 29463
The coexistence of EN 1822 and ISO 29463 at the European level involves EN 1822-1 maintaining its classification system for air filters while adopting the testing procedures specified in ISO 29463 Parts 2-5. The difference in leakage test methods underscores some variability between the two standards in this aspect. While ISO 29463:2017 Part 1 specifies five methods, EN 1822 Part 1 has only three.
| Group | Filter Class | Integral Value | Local Value | |||
|---|---|---|---|---|---|---|
| EN 1822 | ISO 29463 | Collection Efficiency(%) | Penetration% | Collection Efficiency(%) | Penetration% | |
| EPA | E10 | – | 85 | 15 | – | – |
| E11 | ISO 15 E | 95 | 5 | – | – | |
| – | ISO 20 E | 99 | 1 | – | – | |
| E12 | ISO 25 E | 99,5 | 0,5 | – | – | |
| – | ISO 30 E | 99,9 | 0,1 | – | – | |
| HEPA | H13 | ISO 35 H | 99,95 | 0,05 | 99,75 | 0,25 |
| – | ISO 40 H | 99,99 | 0,01 | 99,95 | 0,05 | |
| H14 | ISO 45 H | 99,995 | 0,005 | 99,975 | 0,025 | |
| – | ISO 50 H | 99,999 | 0,001 | 99,995 | 0,005 | |
| UEPA | U15 | ISO 55 U | 99,9995 | 0,0005 | 99,9975 | 0,0025 |
| – | ISO 60 U | 99,9999 | 0,0001 | 99,9995 | 0,0005 | |
| U16 | ISO 65 U | 99,99995 | 0,00005 | 99,99975 | 0,00025 | |
| – | ISO 70 U | 99,99999 | 0,00001 | 99,9999 | 0,0001 | |
| U17 | ISO 75 U | 99,999995 | 0,000005 | 99,9999 | 0,0001 | |
| EN 1822 Part 1:in accordance with filter design | ISO 29463 Part 1:in accordance with filter design |
|---|---|
| Scan leak test | Scan leak test |
| Oil thread leak test | Oil thread leak test |
| Efficiency leak test for 0.3 µm to 0.5 µm | Efficiency leak test for 0.3 µm to 0.5 µm |
| – | Aerosol photometer leak test |
| – | PSL leak test |
What is Integral Value and Local Value for high-efficiency filters per EN 1822-1?
In the context of EN 1822-1:2009, which deals with high-efficiency air filters (EPA, HEPA, and ULPA filters), the terms “Integral Value” and “Local Value” are associated with the assessment of filtration performance, specifically the efficiency of the filters. These values are used in the testing and classification procedures outlined in the standard.
- Integral Value:
The Integral Value, also known as the “Integral Efficiency,” represents the overall efficiency of a filter across a specified range of particle sizes.
It is calculated by integrating the efficiency values over the entire particle size distribution range for which the filter is being tested.
The Integral Value provides a comprehensive measure of the filter’s performance over a broad spectrum of particle sizes, giving a holistic view of its efficiency capabilities. - Local Value:
The Local Value, also known as the “Local Efficiency,” refers to the efficiency of a filter at a specific particle size within the overall particle size distribution range.
It provides information about how effectively the filter captures particles of a particular size.
Local Values are determined at various discrete particle sizes, allowing for a detailed analysis of the filter’s efficiency characteristics at different points in the particle size spectrum.
These values help in understanding the filter’s performance nuances and its effectiveness in capturing particles of specific sizes.
Both Integral Value and Local Value are crucial for assessing the performance of high-efficiency filters because they provide insights into how well the filter captures particles of different sizes. The classification of filters according to EN 1822-1 is based on these values, helping users select filters that meet the requirements of specific applications, especially in critical environments where strict control of airborne particles is essential. The standard defines various classes (E10 to U17) based on the Integral and Local Values, allowing for a systematic and standardized approach to evaluating and specifying high-efficiency air filters.
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