What does MERV mean in air filtration?
MERV stands for Minimum Efficiency Reporting Value. MERV is a rating system developed by ASHRAE (the American Society of Heating, Refrigeration, and Air Conditioning Engineers). The purpose of the MERV system is to measure how well air filters trap particles of varying sizes, otherwise known as filter efficiency. The MERV scale ranges from 1 to 16. The higher the MERV rating, the more efficient the filter is, meaning it can trap smaller particles.
Lower MERV rated filters such as fiberglass and polyester panel filters are intended for equipment protection, i.e. they protect your HVAC equipment from general debris contamination. Higher MERV rated filters are intended to improve air quality in addition to protecting equipment.
Since higher MERV rated (more efficient) filters can trap smaller particles, they can also restrict more air. This problem is solved with pleated filters. Pleating the filter media (folding it like an accordion to fit more media in the filter frame) creates more surface area within the filter, and this allows a greater amount of air to flow through, as opposed to using the same media in a non-pleated flat-panel format. Pleated filters will provide sufficient air flow for a longer period of time than flat panel filters.
Filters are tested for MERV ratings by qualified third party laboratories. Not all filters are MERV rated. If a filter is not MERV rated, it simply means the filter has not been officially tested by a lab against the standards set forth by ASHRAE. This does not mean a filter has not been tested. Some filters are rated under different standards such as HEPA, some manufacturers have their own rating system such as FPR, some products have no rating but still have been tested for pressure drop, dust holding, etc.; it depends on the intended application and design of each product line.
| MERV Rating Chart |
|
MERV Value |
Avg. Particle Size Efficiency % 0.3-1.0 Micron |
Avg. Particle Size Efficiency % 1.0-3.0 Micron |
Avg. Particle Size Efficiency % 3.0-10.0 Micron |
Examples of contaminants trapped |
|
1 |
- |
- |
Less than 20% |
Lint Carpet Fibers Sanding Dust Spray Paint Dust Pollen |
|
2 |
- |
- |
Less than 20% |
|
|
3 |
- |
- |
Less than 20% |
|
|
4 |
- |
- |
Less than 20% |
|
|
5 |
- |
- |
20% - 34% |
Dust Mites Mold Spores Hair Spray Cement Dust Pet Dander |
|
6 |
- |
- |
35% - 49% |
|
|
7 |
- |
- |
50% - 69% |
|
|
8 |
- |
- |
70% - 85% |
|
|
9 |
- |
Less than 50% |
85% or more |
Milled Flour Humidifier Dust Lead Dust Auto Emissions Welding Fumes |
|
10 |
- |
50% - 64% |
85% or more |
|
|
11 |
- |
65% - 79% |
85% or more |
|
|
12 |
- |
80% - 89% |
90% or more |
|
|
13 |
Less than 75% |
90% or more |
90% or more |
Bacteria Virus Carriers Small Allergens Tobacco Smoke / Soot / Smog Smoke |
|
14 |
75% - 84% |
90% or more |
90% or more |
|
|
15 |
85% - 94% |
90% or more |
90% or more |
|
|
16 |
95% or more |
90% or more |
90% or more |
Bonus fact: Air filters become more efficient as debris builds up on the filter. As the filter loads with debris, the debris becomes part of the filter and helps trap even smaller debris. Finally, the filter is too clogged with debris to let enough air flow through. This is why you need to replace your filter at the recommended interval.