MERV Ratings

When you are researching air filters for the first time, you may wonder "what does the MERV number mean?" It can be an important piece of information to know to find the perfect air filter for your warehouse or office building.

Minimum Efficiency Reporting Values (or MERV) ratings indicate a filter's efficiency in capturing airborne particles and contaminants. Some examples are lint, carpet fibers, dust, allergens like pollen and mold, and even bacteria and viruses.

Owners should replace any air filter in their building every 30 to 90 days. This is to ensure the air inside the residential or commercial facility is clean. The date range is based on how often the filter is used.

ASHRAE develops the world-renowned MERV Ratings. ASHRAE stands for American Society of Heating, Refrigerating, and Air Conditioning Engineers.

Ratings are based on rankings in the following criteria:

• MERV rankings range from 1 to 16.
• The higher the MERV rating, the more effective the filter is at trapping small particles (between 0.3 and 10 microns (µm)).
• Any filter with a rating above MERV 6 has to go through an efficiency test.
• Reusable metal filters are generally rated MERV 4 and are not lab-tested.

One primary advantage of having a higher MERV rating is its ability to capture small particles. There would be no concerns in your facility about indoor air contaminants. But, if the MERV rating is too high, it will create a blockage of air flow and will worsen your HVAC system.

On the other hand, a drawback of a high MERV rating is the fact that it will be more expensive to maintain and replace. This is because of the higher amount of contaminants it can catch.

High efficiency particulate air (HEPA) filters demonstrate at least 99.97% efficiency in trapping 0.3 µm particles. These particles can be bacteria, smoke fumes, microscopic dust particles and more.

Usually not given a rating, these filters exceed the ASHRAE test protocol used to determine a MERV rating. These filters have a rating of "MERV 17" or higher because of their high efficiency. Applications that would use HEPA filters include:

• Hospital surgery rooms
• Medical laboratories
• Manufacturing clean rooms
• Medical device manufacturing
• Semiconductor manufacturing
• Pharmaceutical product processing
• Food processing
• Aerospace
• Multi- and single-family homes

The higher the air filter rating, the more air needs force to go through a filter. This is due to the higher pressure drop that comes from a higher MERV rating with filters.

The lower MERV rating leads to less air force required. This results in fewer contaminants trapped in the air filter.

One important factor in deciding on an air filter for your facility is the particles you want to eliminate.

For example, a MERV rating between 1 and 4 are a great choice for filtering out dust, lint and pollen. For dealing with larger contaminants like dust mites and mold, a MERV rating between 5 and 8 can filter out those with ease.

Another factor to keep in mind for choosing a MERV rating is what facility you would like your air filter to be in. 

For example, in an industrial workplace or residential building, MERV 5 to MERV 8 air filters are a great choice. For a smoking lounge, final filter or surgery room, an air filter between MERV 13 and MERV 16 can work the best.

It is important to note what the MERV filter ratings mean and how each filter can work for your business.

The MERV Rating range is between MERV 1 to MERV 16, with HEPA air filters being the highest rated at MERV 17.

No matter what your filtration needs are, The Cary Company has the ideal air filter for your specifications! Browse our selection and find your perfect solution. If you need assistance finding the right filter, please call us at 630.629.6600.