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Guide to MERV Ratings
Reading time: 2 minutes
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What Does a MERV Rating Mean?
Not all air filters are created equal. While most people think “higher is better” when it comes to MERV ratings, the best filter for your application depends on much more than a number. Understanding what a MERV rating measures—and how it affects HVAC performance—is key to choosing the right filtration for your system.
What Is a MERV Rating?
MERV stands for “Minimum Efficiency Reporting Value.” MERV ratings range from 1 to 16. The higher the rating, the smaller and therefore more particulates the filter captures.
For example, a MERV rating of 1 through 4 captures an average particle size of 3.0 - 10.0-micron particle size with less than 20% efficiency. A MERV-13 captures an average particle size of 0.30-1.0-micron with efficiency greater than or equal to 50%, a particle size of 1.0-3.0 microns with efficiency greater than or equal to 85%, and a particle size of 3.0-10.0 microns with efficiency greater than or equal to 90%.
For reference, 0.3 micron is approaching the size of a virus.
Choosing a MERV Rating
Though understanding MERV ratings is fairly easy, selecting the right filter level isn’t as simple as going for the highest value.
Because they are designed with tighter filtration to capture smaller particles, filters with higher MERV ratings also introduce more static pressure to the process of moving air. Not all HVAC units are sized or designed to operate under that added pressure. Using a filter with a MERV rating higher than the unit is recommended for can put a strain on the fan and may cause failure over time. It also can make the fan louder, and a higher MERV rating typically equals a higher cost, as well.
| MERV Rating | Captures | Common Uses |
|---|---|---|
| 1-4 | Large dust, lint | Basic residential |
| 5-8 | Mold spores, dust mites | Better residential, light commercial |
| 9-12 | Lead dust, pet dander | Schools, offices |
| 13-16 | Bacteria, smoke | Hospitals, labs, post-COVID upgrades |
| HEPA | 99.97% of particles ≥ 0.3µm | Clean rooms, operating rooms |
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Generally, residential HVAC units are designed for filters with MERV ratings from 1 to 4. This is sufficient for the day-to-day needs of a home, where primary particulates are dust and pollutants. Residents in high-pollution areas, such as city centers where traffic and dirty air never stop moving, may want to consider upgrading to a unit that can accept a higher-rated filter.
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Traditional commercial projects use filters with MERV ratings from 8 to 13. Post-COVID, many spaces now lean toward the MERV-13 level to better protect occupant health. Spaces with more sensitive occupants or that are more prone to germs, such as schools, may want to consider ratings of MERV-13 or higher.
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Some commercial projects that use or manufacture sensitive equipment, such as a battery plant, will look to MERV-16 filters. Units using this level of filtration will require a lot more power to move air.
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Finally, for ultra-sensitive applications like clean rooms and operating rooms, filtration moves from a MERV-rated filters to HEPA (“High Efficiency Particulate Air Filter”) pleated mechanical air filters. These filters capture at least 99.97% of dust, pollen, mold, bacteria, and any airborne particles with a size of 0.3 micron, per the EPA.
Keep in mind that MERV filtration can vary across one project, depending on its use. Ventilation for a dentist’s waiting room may not require as sensitive of filtration as the examination rooms, for instance.
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Other Considerations for Choosing a Filter
Along with MERV ratings, specifiers should consider a filter’s depth. A deeper filter, at 4”, will be pleated, so it can help with static pressure while still capturing particulates. Like the MERV ratings, a unit must be designed to accept these deeper pleated filters.
One of the biggest errors people make with air filters is that the air is moving through them too quickly. MERV ratings are based on a certain air velocity. Forcing faster air through pressurization will result in a lower capture rate. The higher the MERV, the lower the velocity should be, so a MERV 1-4 may go 300-500 fpm; however a MERV16, for example, may be 200-400 fpm.
Connect With Systemair for Filtration Flexibility
Systemair’s versatile array of air handling units can accommodate a range of applications and MERV filtration needs. Reach out to us to get started.
What Else Is Changing in HVAC?
While filtration standards evolve, so do the refrigerants running through modern HVAC systems.
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