During the process of recirculating clean air into a room, air filters trap minuscule particles, such as dust, dander, and even microorganisms. ASHRAE says that this kind of filtration improves air quality in factories, warehouses, and homes.
However, the efficiency of a filter is dependent on the filter’s design. The MERV rating of a filter shows how well it can remove these particles. However, MERV is still generally unknown by the wider public. In this guide, we’ll briefly go over what the MERC rating chart is, and how MERV filters differ from HEPA.
| MERV Rating | Air Filter will trap Air Particles size .3 to 1.0 microns | Air Filter will trap Air Particles size 1.0 to 3.0 microns | Air Filter will trap Air Particles size 3 to 10 microns | Filter Type – Removes These Particles |
| MERV 1 | < 20% | < 20% | < 20% | Fiberglass & Aluminum Mesh |
| MERV 2 | < 20% | < 20% | < 20% | |
| MERV 3 | < 20% | < 20% | < 20% | Pollen, Dust Mites, Spray |
| MERV 4 | < 20% | < 20% | < 20% | Paint, Carpet Fibers |
| MERV 5 | < 20% | < 20% | 20% – 34% | Cheap Disposable Filters |
| MERV 6 | < 20% | < 20% | 35% – 49% | |
| MERV 7 | < 20% | < 20% | 50% – 69% | Mold Spores, Cooking Dusts |
| MERV 6 | < 20% | < 20% | 70 – 85% | Hair Spray, Furniture Polish |
| MERV 9 | < 20% | Less Than 50% | 85% or Better | Better Home Box Filters |
| MERV 10 | < 20% | 50% – 64% | 85% or Better | |
| MERV 11 | < 20% | 65% – 79% | 85% or Better | Lead Dust, Flour |
| MERV 12 | < 20% | 80% – 90% | 90% or Better | Auto Fumes,Welding Fumes |
| MERV 13 | Less Than 75% | 90% or Better | 90% or Better | Superior Commercial Filters |
| MERV 14 | 75% – 84% | 90% or Better | 90% or Better | |
| MERV 15 | 85% – 94% | 95% or Better | 90% or Better | Bacteria, Smoke, Sneezes |
| MERV 16 | 95% or Better | 95% or Better | 90% or Better | |
| MERV 17 | 99.97% | 99% or Better | 99% or Better | HEPA & ULPA |
| MERV 16 | 99.997% | 99% or Better | 99% or Better | |
| MERV 19 | 99.9997% | 99% or Better | 99% or Better | Viruses, Carbon Dust, <.30 pm |
| MERV 20 | 99.99997% | 99% or Better | 99% or Better |
What Exactly Is MERV?
The minimum efficiency reporting value (MERV) of an air filter indicates how well the filter prevents dust and other airborne particles from recirculating into the air. MERV ratings are used to determine how well a filter traps smaller particles.
MERV rating charts display the efficiency of a product by displaying the figure on the chart. There are 20 points on the chart, with 1 representing the lowest efficiency and 20 representing the highest efficiency.
Looking at MERV Ratings and Efficiency Levels
It’s important to remember that when selecting the best filter for your application, bigger is not always better. Using an air filter with a higher MERV rating than the one recommended by the manufacturer of your furnace or air conditioner can actually reduce the performance of your equipment by as much as 10%.
More highly rated air filters have smaller pores, which creates resistance to airflow. When used in an HVAC system that is not designed to withstand this resistance, the filter can reduce system efficiency, degrade indoor air quality, and place additional strain on the fan motor.
Now let’s take a closer look at the MERV ratings and see how effective they really are:
- MERV 1-4 < 20% for 3-10-micron particles
- MERV 6 ≤ 49.9% for 3-10-micron particles
- MERV 8 ≤ 84.9% for 3-10-micron particles
- MERV 10 ≤ 64.9% for 3-10-micron particles and ≤ 85% for 10-micron particles and larger
- MERV 12 ≤ 89.9% for 1-3-micron particles and ≤ 90% for 3-micron particles and larger
- MERV 14 ≤ 84% for 0.3-1-micron particles and larger and ≤ 90% for 1-3-micron particles
- MERV 16 ≤ 75% for 0.3-1-micron particles and larger
A Higher MERV (M) value of a filter shows a more efficient filter. Filters with M values between 1 and 4 capture large particles. These filters are mostly used to keep personal protection equipment safe.
You will most likely find them in use at small-scale industrial plants and home projects. Between 3 and 10 microns, they aren’t very efficient at all. MERV 1 to 4 is given if the average arrestance value is at least 4. The lint trap in a dryer, for example, is about M 2.
It’s easier for filters with an M value of 5 to 8 to get rid of smaller debris of dust. Smaller particles have a greater chance of getting stuck in your lungs. In order to help keep people and their homes safe from airborne particles, this type of air filter will come into play.
Particle Size Ranges
| Range | Size in microns | Group |
| 1 | 0.30 to 0.40 | E1 |
| 2 | 0.40 to 0.55 | |
| 3 | 0.55 to 0.70 | |
| 4 | 0.70 to 1.00 | |
| 5 | 1.00 to 1 30 | E2 |
| 6 | 1.30 to 1.60 | |
| 7 | 1.60 to 2.20 | |
| 8 | 2.20 to 3.00 | |
| 9 | 3.00 to 4.00 | E3 |
| 10 | 4.00 to 5.50 | |
| 11 | 5.50 to 7.00 | |
| 12 | 7.00 to 10.00 |
Filters with an M rating of 9 to 12 can be used in most homes. They get rid of most of the dust in homes and places of work: They also let cool air pass, making them perfect for recirculating air into hot rooms. Their prices are often reasonable and can fit into a wide range of budgets.
Filters with an M rating of 13 to 16 are thought to be significantly better than the previous ratings. Due to their smaller pores, they need special blowers to recirculate clean air throughout a room. It’s very important not to use these filters in a home’s air conditioner or heater. They are usually used for high-end business applications.
Filters with M ratings of 17 to 20 are no longer available as a new filter type has rendered them obsolete. While this level of filtration efficiency is displayed on the chart, you cannot find such a filter in today’s market. In the past, M 17 to 20 filters were known to capture most dust, viruses, and hazardous materials.
Composite Average Particle Size, % in size Range
| MERV Value | 0.3 – 1.0 | 1.0 – 3.0 | 3.0 – 10.0 | Arrestance |
| 1 | n/a | n/a | E3<20 | 60(avg)<65 |
| 2 | n/a | n/a | E3<20 | 65(avg)<70 |
| 3 | n/a | n/a | E3<20 | 70(avg)<75 |
| 4 | n/a | n/a | E3<20 | 7S(avg)<80 |
| 5 | n/a | n/a | 20<E3 | n/a |
| 6 | n/a | n/a | 35<E3 | n/a |
| 7 | n/a | n/a | 50<E3 | n/a |
| 8 | n/a | 20<E2 | 65<E3 | n/a |
| 9 | n/a | 35<E2 | 80<E3 | n/a |
| 10 | n/a | 50<E2 | 85<E3 | n/a |
| 11 | 20<E1 | 65<E2 | 90<E3 | n/a |
| 12 | 35<E1 | 80<E2 | 90<E3 | n/a |
| 13 | 50<E1 | 85<E2 | 95<E3 | n/a |
| 14 | 75<E1 | 90<E2 | 95<E3 | n/a |
| 15 | 85<E1 | 90<E2 | 95<E3 | n/a |
| 16 | 95<E1 | 95<E2 | 95<E3 | n/a |
How Does MERV Compare to HEPA?
High Efficiency Particulate Air (HEPA) is a mechanical filter that must remove 99.97%of particles 0.3 microns in size. As shown, HEPA filters outperform MERV 0.3-1-micron particle size filters by a significant margin.
The great thing about HEPA filters is that they’re not just for factories. Many modern air purifiers have HEPA filters to trap common allergens like pollen and dander. Homeowners claim that purchasing a HEPA air purifier significantly improved their quality of life.
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