In the 1950s, replacing an air filter required practically no thought. You would remove the dirt- and dust-covered fiberglass filter and replace it with a new filter. Today, choosing the right filter for your home or business requires a lot of thought. Over 25 years ago, ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) also recognized the need to normalize the filter playing field. MERV (Minimum Efficiency Reporting Value) was developed and instituted as a method to compare the effectiveness of one filter against another.

MERV uses a common rating system of 1 to 20. Filters with higher MERV ratings provide better filtration. The lower MERV ratings are least effective at filtration. Filtration is based on particle size in micrometers (um).  As an illustration, a single human hair is approximately 20 micrometers, and a single red blood cell 8 micrometers in size.

The following list provides samples of MERV ratings, environments where filters may be found, and the filter’s particle-capture ability.

  • MERV 19: Electronics manufacturing (less than 0.3 um)
  • MERV 17: Surgical suite (.6 um)
  • MERV 13: Superior residential (1.5 um)
  • MERV 9:   Business (8.0 um)
  • MERV 2:   Minimal filtration (greater than 10 um)

Don’t be misled by flashy advertising. Some filters claiming to be “HEPA” really aren’t HEPA at all. A filter must have a MERV rating between 17 and 20 to qualify as a true HEPA filter. True HEPA filters provide the best filtration by capturing the smallest airborne pollutants and contaminants.  These filters can capture as much as 99.9 percent airborne particles.

HEPA filters are a great alternative when regular filters aren’t enough. You may be surprised to learn that air filters with MERV ratings between 8 and 16 are capable of trapping particles as small as mold spores. Filters with lower MERV ratings are able to capture smoke, odors, dust, pet hair and dander and pollen.

The NATE-certified professionals at Paschal Heat & Air Conditioning are ready to answer your MERV questions. We can help you choose the right air filter for your home or business.

Our goal is to help educate our customers about energy and home comfort issues (specific to HVAC systems).  For more information, click here to download our free Home Comfort Resource guide.

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