Air filters capture and collect large and small particles, such as dust, allergens and microorganisms, as air passes through a building's HVAC system. According to the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), this filtration helps provide healthier indoor air quality. The filter's MERV number indicates how it removes these particles.
But what exactly is a MERV rating?
An air filter's Minimum Efficiency Reporting Value (MERV) rating measures how effectively a filter prevents dust and other contaminants from passing through the filter and into the air flow. Filters with higher MERV ratings capture small particles more effectively than filters with lower MERV ratings.
Generally, filters rated MERV 16 or below are considered HVAC system grade filters for residential, commercial and general hospital use. MERV 17 to MERV 20 filters are typically used in surgical operating rooms, clean rooms and other environments where absolute cleanliness is required.
MERV Filter Rating and Efficiency
When choosing the right filter for your application, higher is not necessarily better. Using an air filter with a higher MERV rating than your furnace or air conditioner manufacturer recommends can actually harm its performance.
Smaller pores in higher-grade air filters can create airflow resistance, and if the filter is used in an HVAC system not designed to handle this resistance, it can reduce the efficiency of the system, reduce indoor air quality, and cause adverse effects on air flow. Fan of the pressure system.
MERV filter rating and air quality
A position paper published by ASHRAE looks at the health benefits of particle filtration. According to the paper, there is a clear link between higher concentrations of particulate matter in outdoor air and adverse health outcomes, so it makes sense that filtering these particles out of indoor air could lead to better health outcomes.
The ASHRAE paper reviews research showing:
Particulate filtration can be "moderately effective" against allergy and asthma symptoms. Particle filtration can reduce the concentration of infectious airborne particles that transmit many infectious diseases, which is why some models suggest it can "dramatically reduce the portion of disease transmission caused by these small particles." The health benefits of particle filtration are proportional to "reduced total exposure to particles smaller than 2.5 µm in diameter". Use the MERV rating table below to learn which filters are best for which applications.
Use the MERV rating chart below to understand which filters are best for which applications.
MERV Rating Chart
|
MERV Rating |
Description |
Application |
Typical Air Filter Material |
|
MERV-1 to MERV-4 |
N Cuts down on carpet fuzz and lint, but doesn't block much else. |
ü Pre-Filter In Commercial Building ü Residential Furnaces ü Window Air-Conditioning Unit |
ü Fiberglass ü Washable aluminum ü Synthetic mesh · |
|
MERV-5 to MERV-8 |
Representative filter Keeps away common dust, pollen, and some mold spores. |
ü Pre-filters or Final Filters ü Commercial Buildings ü Industrial Workplaces ü Paint Booth Inlets |
ü Pleated cotton ü Polyester · |
|
MERV-9 to MERV-12 |
Good filter Filters out most common air pollutants, such as mold spores, smog, fine dust, and pet dander. |
ü Hospital Laboratories ü Better Commercial Buildings ü Superior Residential Buildings |
ü Pleated cotton ü Microfine fiberglass ü Usually 2" thick or more · |
|
MERV-13 to MERV-16 |
Better filter Stops tiny airborne things like bacteria, viruses, and smoke. |
ü General Surgery ü Superior Commercial Buildings ü Hospital Inpatient Care ü Smoking Lounges |
ü Pleated cotton ü Microfine fiberglass ü Usually 4" thick or more |
Air filter MERV Rating Table
The table below shows the minimum threshold that a filter must perform at in order to obtain a specified MERV rating. As the MERV rating goes up, the filtration efficiency requirements get more stringent.
Minimum % of particles removed by air filter
|
MERV Rating |
E1 particles (0.3 - 1.0 microns) |
E2 particles (1.0 - 3.0 microns) |
E3 particles (3.0 - 10.0 microns) |
|
MERV-1 to Merv-4 |
- |
- |
<20% |
|
MERV-5 |
- |
- |
>20% |
|
MERV-6 |
- |
- |
>35% |
|
MERV-7 |
- |
- |
>50% |
|
MERV-8 |
- |
>20% |
>70% |
|
MERV-9 |
- |
>35% |
>75% |
|
MERV-10 |
- |
>50% |
>80% |
|
MERV-11 |
>20% |
>65% |
>85% |
|
MERV-12 |
>35% |
>80% |
>90% |
|
MERV-13 |
>50% |
>85% |
>90% |
|
MERV-14 |
>75% |
>90% |
>95% |
|
MERV-15 |
>85% |
>90% |
>95% |
|
MERV-16 |
>95% |
>95% |
>95% |
The highest MERV rating must not only be able to filter smaller particles but many more as well.
MERV 1 filters have not been tested for their ability to catch the particles which are both E1 and E2. This does not mean that these filters will not catch any E1 or E2 particles- they have just not been tested.
