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If you have been shopping for air filters, you’ll notice that there are a few different rating systems out there. Even though they have completely different numbers, they are still air filters and can be compared directly against each other.
In this article, we’ll take a look at the differences between two of the most common air filter rating systems– MERV and MPR. We’ll make sense of these two systems and compare them to each other to show you what they measure, how they measure it, and what their differences are.
Differences between MERV and MPR filter rating systems
The main differences between the MERV and MPR filter rating systems are as follows:
- The MERV rating system is the industry-standard rating system. It was established by the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE).
The MPR rating system was created by 3M to measure an air filter’s effectiveness at filtering out microparticles.
- The MERV rating system establishes minimum percentages of particles that a filter must trap in order to obtain a MERV rating. For instance, a filter with a MERV rating of MERV-13 must be able to trap at least 50% of E1, 85% of E2, and 90% of E3 particles.
The MPR rating system is focused on measuring a filter’s effectiveness at capturing the tiniest particles – E1 particles. For instance, an MPR 1000 filter is able to filter 41% of E1, 77% of E2, and 88% of E3 particles. However, it is not clear what 3M’s guidelines are for giving different filters a specific MPR rating.
Even though MERV and MPR are different rating systems, some filters that are rated by each of these systems are directly comparable to each other.
For instance, a MERV-13 filter is very similar to an MPR 1500 filter in terms of how effective they are at capturing particles of E1, E2, and E3 sizes.
What is the MERV filter rating system?
The Minimum Efficiency Reporting Value, or MERV rating system is defined in ASHRAE standard 52.2. It is the industry-standard air filter rating system.
ASHRAE 52.2 defines the performance level that a filter must achieve to obtain a certain MERV rating. ASHRAE 52.2 also defines the testing procedures that are required for a filter to obtain a MERV rating.
The MERV rating scale defines the minimum percentage of particles that must be trapped by an air filter in order to obtain a particular rating. The MERV rating scale goes from MERV-1 to MERV-16, with MERV-16 providing the best filtration on the MERV scale.
For instance, in order for a filter to obtain a MERV-13 rating, the filter must be able to capture at least 50% of E1 particles, 85% of E2 particles, and 90% of E3 particles. See our section below on the differences between E1, E2, and E3 particles.
The table below shows what percentage of particles must be trapped in order to obtain each MERV rating.
MERV Rating Table
Minimum % of particles removed by air filter
(0.3 - 1.0 microns)
(1.0 - 3.0 microns)
(3.0 - 10.0 microns)
How does the MPR filter rating system work?
The MPR, or Microparticle Performance Rating system is designed to measure an air filter’s filtration of microparticles. Specifically, the system focuses on measuring a filter’s efficacy for particles in the 0.3 to 1.0 micron range.
These tiny particles of particulate matter are found in the air. These particles can be inhaled and cause health concerns. Particles less than 10 micrometers are able to get into your lungs. Some of them are even able to get into your bloodstream.
Particulate matter that is less than 2.5 micrometers in diameter poses the greatest risk to your health. This type of particulate matter, also known as PM2.5, is the primary cause of haze in the United States.
The MPR filter rating system is intended to measure a filter’s effectiveness for particles in the PM2.5 range. Since particles in this range are the cause of health problems, filtering them out will improve the air quality inside your home and help prevent health issues that stem from microparticles.
The MPR rating system is measured on a scale from MPR 300 to MPR 2800. The higher the MPR number, the greater the filter’s effectiveness at removing tiny airborne particles.
For instance, a filter with a rating of MPR 2200 is able to remove 69% of E1 particles– particles in the 0.3 to 1.0 micron range.
What about HEPA filters?
HEPA filters are a different beast altogether. HEPA filters are not reflected on the MERV rating scale because they exceed the testing requirements set forth by ASHRAE 52.2.
HEPA filters are tested and certified to filter out at least 99.97% of 0.3 micron particles. 0.3 micron particles are the smallest particles that are tested by the MERV rating scale.
For comparison, MERV-16 filters are rated for only capturing >95% of E1 particles, which include particles between 0.3 and 1.0 microns. HEPA filters are able to filter out 99.97% of the smallest E1 particle on the MERV scale. A truly incredible feat.
But just because HEPA filters have the best filtration, doesn’t mean that you should use them in your home’s HVAC system. HEPA filters are typically only used for the absolute most stringent environments– such as hospital operating rooms, clean rooms for computer chip manufacturing, etc.
If you tried to use a HEPA filter in your home’s furnace, the airflow restriction from the filter would probably burn out your blower motor in no time at all. A typical residential HVAC system is simply not designed for running with a HEPA filter.
ASHRAE 52.2 testing procedure for air filters
ASHRAE standard 52.2 also defines the methods for testing filter efficiency by particle size. These methods must be used in order for a filter to obtain a valid MERV rating.
To test a filter, an aerosol generator is used to spray particles of known sizes into an air stream. As the air flows through a test duct, it passes through the filter, and some of the particles become trapped in the filter.
The air filter’s performance is determined by counting the particles before and after the filter. Six tests are done on a single filter– the test is started with a clean filter, then that same filter is used for five additional tests.
For each of these tests, the filtration efficiency is calculated as the ratio of particles measured after the filter to particles measured before the filter. Basically, the more particles that were trapped in the filter, the higher the filter’s efficiency.
There are twelve different size ranges of particles that are tested. Each of these size ranges is put into one of three different groups: E1, E2, and E3. Calculating the average minimum efficiency for each of these three groups determines the average particle size efficiency for that particular group.
E1 vs. E2 vs. E3 particles
E1, E2, and E3 are the three different size groups of particles that are tested with air filters. The particle removal rate of air filters is tested using these three different size groups to determine their efficiency.
Particle size ranges for E1, E2, and E3 particles
Particle Size Range
Particle Diameter (microns)
0.30 to 0.40
0.40 to 0.55
0.55 to 0.70
0.70 to 1.00
1.00 to 1.30
1.30 to 1.60
1.60 to 2.20
2.20 to 3.00
3.00 to 4.00
4.00 to 5.50
5.50 to 7.00
7.00 to 10.00
The E1, E2, and E3 particle groups are determined by ASHRAE standard 52.2. The testing factors for ASHRAE 52.2 were developed to provide filter efficiency data for different particle sizes. The goal of these tests is to give an accurate representation of an air filter’s performance at removing particles of different sizes.
The diagram below shows a comparison between the sizes of E1, E2, and E3 particles. Also shown is the cross-sectional diameter of a human hair, which is much larger than any of those particles.
PM10 particles are typical particles in the E3 range. The size of these particles is typical of dust, pollen, and mold spores.
PM2.5 particles consist of mostly E2 and E1 particles. Typical E2 particles are pet dander and some larger bacteria, such as E. coli.
E1 particles are representative of extremely small particles such as smoke, haze, bacteria, and some viruses. These are the smallest particles that are measured on the MERV and MPR scales. Particles smaller than 0.3 microns are not measured on either of these scales.