Demystifying Air Filter Rating Scales
Air filtration plays a crucial role in maintaining indoor air quality, whether it’s in residential, commercial, or industrial settings. When selecting the right air filter, understanding various rating systems can help you choose the most appropriate filter for your needs. Universal Air Filter (UAF) is a custom filter manufacturer that can meet your entire range of needs depending on the application, without limiting our customers to standard “off-the-shelf” options. Many of our customers face challenges in understanding filter efficiency requirements and the terminology used in different regions such as the EU, North America, and APAC.
Our goal is to help eliminate some of that confusion and provide our customers with a reference tool for understanding the most common air filter rating scales. By breaking down these various standards, UAF aim’s to make it easier for you to select the right filter for your application, ensuring optimal performance.
ASHRAE 52.1
ASHRAE (American Society of Heating, Refrigerating, and Air-Conditioning Engineers) 52.1 is one of the earlier air filter standards and focuses on two main criteria:
- Arrestance: This measures the filter’s ability to remove synthetic dust from the air.
- Dust Spot Efficiency: This assesses how well the filter removes smaller dust particles by measuring staining on a test surface.
While ASHRAE 52.1 helped establish baseline performance, it has been largely replaced by the more modern ASHRAE 52.2 standard. However, it’s still in use for older systems or for those that rely on specific legacy ratings.
ASHRAE 52.2
ASHRAE 52.2 was developed to modernize and provide more consistent evaluations of air filter performance. The key element of ASHRAE 52.2 is the Minimum Efficiency Reporting Value (MERV) rating, which classifies filters based on their ability to capture particles within three distinct size ranges:
- 0.3 to 1.0 microns
- 1.0 to 3.0 microns
- 3.0 to 10 microns
The MERV scale ranges from 1 to 20, with higher numbers indicating better filtration efficiency. For example, a filter with a MERV rating of 8 is adequate for most residential settings, while hospitals often use filters rated MERV 13 or higher to capture smaller particles like viruses and bacteria.
EN779
EN779 was the European standard for air filter testing, prior to being replaced by ISO 16890. EN779 classified filters into three categories:
- G1 to G4 (Coarse filters)
- M5 to M6 (Medium filters)
- F7 to F9 (Fine filters)
The classification was based on a filter’s ability to capture particles between 0.4 to 10 microns in size. Like ASHRAE 52.1, EN779 had limitations, particularly in the way it measured real-world performance across various particle sizes, which led to its replacement by ISO 16890.
ISO 16890
ISO 16890 is now the global standard, replacing EN779 in Europe and used widely across the world. It categorizes filters based on their ability to capture particulate matter of different sizes:
- PM10 (particles ≤ 10 microns)
- PM2.5 (particles ≤ 2.5 microns)
- PM1 (particles ≤ 1 micron)
Filters are tested across a range of particle sizes and classified based on the percentage of particles they remove from each size range. This makes ISO 16890 more aligned with real-world conditions, since it considers performance across the entire spectrum of particle sizes.
Comparing the Rating Systems
To help you visualize the equivalent ratings between these systems, here is a comparison table:
| ASHRAE 52.1 (Dust Spot Efficiency) | ASHRAE 52.2 (MERV Rating) | EN779 Rating | ISO 16890 Equivalent |
| 20-35% | MERV 6 | G3 | ISO Coarse (50-65% PM10) |
| 35-50% | MERV 7-8 | G4 | ISO Coarse (65-85% PM10) |
| 50-70% | MERV 9-10 | M5 | ePM10 50% |
| 70-85% | MERV 11-12 | M6 | ePM10 60-70% |
| 85-95% | MERV 13-15 | F7 | ePM2.5 50% / ePM1 50% |
| >95% | MERV 16+ | F8, F9 | ePM1 65-80% |
Key Takeaways
Each air filter rating system has its own focus, from legacy dust arrestance in ASHRAE 52.1 to the comprehensive real-world performance assessment in ISO 16890. With newer systems like ASHRAE 52.2 and ISO 16890, you get a better understanding of how well a filter will perform in different environments and particle size ranges. As the global standard, ISO 16890 now offers the most accurate representation of a filter’s performance across various particle sizes, making it the go-to rating for choosing an air filter today.
Universal Air Filter can help you identify the proper level of protection for your application based on several key factors such as the components being protected, the operating environment, air flow, and your desired maintenance intervals. By considering these elements alongside the appropriate air filter rating, UAF ensures you get optimal filtration performance, which enhances air quality and extends the lifespan of your equipment.
Whether you’re in charge of air quality in a home, business, or industrial facility, keeping up with these rating systems and partnering with experts like UAF is essential for making informed decisions about your filtration needs. Get in touch with us today!