MERV Ratings: What Do They Mean?

new furnace filter on white background

MERV Ratings: What Do They Mean?

Every homeowner and building manager buys air filters. Maintenance teams, business tenants, home renters, and repair services; we all buy air filters. Why? Because indoor air quality is important – and every HVAC system in the modern world requires the constant changing of air filters. Air quality and circulation efficiency both depend on a clean, unclogged air filter as part of the system – and anyone responsible for their building or zone’s air quality takes on changing that filter.

To buy an air filter refill pack, you need your unit’s filter size and your desired MERV rating.  The size you can get from your unit specs. But what is MERV? How do you choose the right MERV  for your building, and just how much does it matter?

Here is the meaning of air filter MERV ratings.


MERV Stands for Minimum Efficiency Reporting Values

So what is a MERV rating? MERV stands for Minimum Efficiency Reporting Values. The MERV rating measures a filter’s ability to stop and contain airborne particles between 0.3 and 10 microns large.  This is the range that includes dust, mites, pollen, mold spores, and can even include some microbiology like bacteria cells in the are.

MERV ratings range from 1-20. Lower MERV ratings stop only large particles like dust motes and balls of pollen. Higher MERV ratings stop all particles down to a much smaller size, including microbiology.


The MERV Rating Chart for Air Filters

  • MERV 1 – MERV 4
    • Filters 3-10 microns at 20% efficiency
  • MERV 6
    • Filters 3-10 microns at 50% efficiency
  • MERV 8
    • Filters 3-10 microns at 85% efficiency
  • MERV 10
    • Filters 1-3 microns at 50%-65% efficiency
    • Filters 3-10 microns 85% plus efficiency
  • MERV 12
    • Filters 1-3 microns at 80%-90% efficiency
    • Filters 3-10 microns at 90% plus efficiency
  • MERV 14
    • Filters 0.3 – 1 microns at 75%-85% efficiency
    • Filters 1-3 microns at 90% plus efficiency
  • MERV 16
    • Filters 0.3-1 microns at 75% plus efficiency

Microns and Efficiency

So what exactly do these MERV ratings mean? The microns indicate just how small of particles will be stopped by the filter. The percentage indicates how many of those particles are likely to be stopped. For example, MERV 6 stops particles sized 3-10 microns at 50% efficiency. That means about half of all particles in this size range (or larger) will be caught by the filter. It will take several cycles through the filter to remove most particles in this size range.

MERV 10 filters 3-10 micron particles at 85% efficiency, and can stop even smaller particles at about 50% efficiency. So 85% of larger particles and half of smaller particles are stopped with each pass.

Chain-Link Fence Analogy

Think of your air filter as a chain-link fence. At first, you can push tennis balls, ping pongs, and marbles through. A tighter woven fence, the tennis balls won’t go through, but the ping pongs and marbles will. A fence with very tight weave won’t allow a marble through, but wind still blows through the fence.

On a much smaller scale, that’s exactly what a MERV-rated air filter is doing. As the MERV scale goes up, the filter is tighter to stop more and smaller unwanted air particles. However, as you might imagine, the tighter the weave, the more likely a filter will become clogged and need regular changing.


Low MERV,  Average Air Quality

Low MERV filters are the standard. Most homes and businesses maintain good air quality with regularly changed filters on the low-end of the MERV rating scale. Lower MERV filters are more affordable because they are not as dense as high MERV-rated filters and require less specific materials to filter out the smaller particles and microbiology.

MERV ratings of 1-8 are commonly used for residences and businesses. They are good for filtering the usual suspects when it comes to poor air quality. This includes

  1. Pollen
  2. Dust mites
  3. Sawdust
  4. Lint and carpet fibers
  5. Household dust
  6. Mold spores
  7. Concrete dust


Medium MERV, High Air Quality

MERV ratings between 8 and 12 are considered to create high air quality. Filtering particles as small as 1 micron, Merv 8-12 is typically used by hospitals and laboratories along with residential and commercial buildings seeking especially clean air. For the most part, non-laboratory spaces don’t need a MERV of higher than 12, so unless you’re running an ICU or a pharmaceutical lab, you don’t need to worry about filters of a higher rating.

MERV between 8 and 12 filter out very small particles with increasing efficiency including

  1. Legionella
  2. Lead dust
  3. Coal dust
  4. Nebulizer dust
  5. Humidifier dust


High MERV, Medical Grade Air Quality

For facilities that require superb air quality and clean-room level safety, you can seek MERV higher than 12. Considering that MERV can go all the way up to 20 (though rarely seen above 16) there are still a lot of very tiny particles to filter – but most don’t directly interfere with human life.

MERV ratings above 12 are typically used for clean rooms, pharmaceutical manufacturing, surgery facilities, inpatient care hospitals, and control of radioactive or carcinogenic storage/processing areas.

In these ranges, filters also block

  1. Radon progeny
  2. Virus particles
  3. Copier ink fumes
  4. Carbon dust
  5. Microscopic allergens
  6. Bacteria


What MERV Rated Filter Does Your Building Need?

If you are responsible for stocking and replacing the air filters in your building, choosing the right MERV rating is essential. Many homes and businesses use MERV 1-4 to filter out the usual dust, dander, and carpet fibers and prevent dust from building up inside the building. For a higher level of air quality without overpaying for filters, MERV ratings 8-12 are a great choice to filter smaller air particles and increase the total percentage of particles removed from your air with each pass.

Consider the cleanliness and health needs of your building and the dust-generating sources. Increase your MERV rating if there are sick people who need protection, or extra sources of dust like pets or construction. Increase your MERV rating if there’s been air quality concerns in the building or certain air quality metrics you need to meet.

Which MERV-rated air filter is the right choice for your HVAC filter replacements? It all depends on the needs of your building.

If you’re interested in learning more, give LEGACY a call at (725) 237-2441.

Share this post