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Selecting the Best Air Filter for Your System -- How HEPA and MERV Factor In

  • Air Conditioning

Filters keep debris out of HVAC systems and prevent pollutants from compromising your indoor air quality. Not all filters are created equal, however. Choosing the right kind is important. Here are tips for selecting the best air filter.

Are high efficiency filters preferable over standard filters?

A regular, flat fiberglass filter is inexpensive, and it will filter some particles. However, it will not keep your system nor your home as clean and pollutant free as high efficiency filters. Although high efficiency filters cost more than low efficiency filters, your system and home will be better protected. High efficiency filters trap more pollutants, keeping the machinery and airflow cleaner, which results in better operation of your heating and cooling system and a healthier home environment. In the end, paying a little extra is worth it.

High efficiency air filters


The term, “HEPA filter,” stands for High Efficiency Particulate Air filter or High Efficiency Particle Arresting filter. It is important to note that HEPA filters are not the only high efficiency filters. HEPA is the name given to types of filters that have undergone strict testing assuring that they trap very tiny particulates, down to 0.3 microns in size with nearly 100 percent efficiency. Other high efficiency filters have 60 to 95 percent efficiency for filtering particle sizes between 0.3 and 10 microns, while medium efficiency filters have 20 to 50 percent efficiency.

  • How to determine whether a filter is a HEPA filter -- True HEPA filters are labeled with special certification labels.
  • Can HEPA filters be used with my existing system? -- Although HEPA filters are helpful in controlling allergens, they pose a problem for many HVAC systems. In order for a system to work effectively and safely, air must be able to flow through the filter at a certain rate. The tight weave of a HEPA filter creates airflow resistance that renders systems unequipped for this inoperable or dangerous. Before buying a certified HEPA filter, you should always check with an HVAC contractor or your system’s manufacturer to see if it is HEPA compatible. When selecting the best air filter, HEPA may not be the one for you.
  • Where are HEPA filters usually used? -- Medical and industrial facilities use HEPA filtration to clean the air of contagions and toxins. HEPA filters are also used in some vacuum cleaners and portable air cleaners.  

MERV rating

Non-HEPA filters are rated according to their Minimum Efficiency Reporting Value (MERV). The higher the number, the more efficient a filter is at capturing tiny particles from the air.

Selecting the best air filter does not mean choosing those with the highest MERV rating, however. The reason for this is the same given concerning HEPA filters. The higher the efficiency, the greater the airflow resistance. Your existing system may not be able to handle filters rated over MERV 13, for example. Most systems are compatible with filters rated between 8 and 13.

For most home HVAC systems, a filter efficiency rating of 11 is adequate for sustaining good indoor air quality. While MERV 11 is considered medium efficiency, studies show that it offers nearly the same protection from allergens as higher efficiency filters but without the airflow resistance problems.

Caring for filters

  • Among the most frequently asked questions homeowners have about ductless systems is regarding necessary maintenance. The primary thing you should do to maintain any heating, cooling or ventilation system is to change or clean filters regularly. Most filters should be checked once a month.
  • Clogged filters lower efficiency and present problems for equipment. Filthy filters may also release some of the allergy-promoting particles into the home’s air supply.
  • If the manufacturer has indicated a specific efficiency rating, do not choose a filter that exceeds that. Doing so may cause problems and void any warranty you have.
  • Choose the right filter size for your system and make sure it fits snugly to prevent air leaks.   

To learn more about selecting the best air filter or about ways to increase home comfort, or to find a Mitsubishi Electric contractor in your area, please contact today.


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