How Are Air Conditioner/Furnace Filters Rated?

To understand the varying qualities of air conditioner filters you first need to understand the ‘MERV’ scale. The MERV scale, also known as Minimum Efficiency Reporting Value, is based on the percentage of particles from 0.3 to 10 microns in size that are filtered out of your system. The higher the MERV number on your filter then the better your air quality will be. Along with the MERV rating there is another measurement known as MPR or Microparticle Performance Rating. This MPR scale measures very small particles between 0.3 and 1.0 microns. Just like with MERV, the higher the MPR number the smaller the items that are filtered.

There are a variety of MERV sized air filters. To give you an example of the range let’s take a look below:

  • MERV One Through Four Filters – These are your lower end models that you’ll find in most grocery stores. While they do provide you with a filter, it is only the bare minimum. They can trap pollen and mold spores, but not near as well as higher rated filters. They are rated to remove particles over ten microns in size.
  • MERV Five Through Eight Filters – This is the next step up and will allow you to see a noticeable difference from the previous rung. These filters will allow you to remove agitants up to three microns in size. This would cover your pollen and mold spores as well as certain types of bacteria.
  • MERV Nine Through Twelve Filters – Now we’re getting into the higher quality air filters. These filters are rated to remove particles as low as one micron in size.  This could include such things as human hair, dust, pollen, mold, and combustion particles from candles or indoor fireplaces.
  • MERV Thirteen Through Sixteen Filters – Ok, folks this is the highest of the high for residential air conditioning and heating. With this rating we can get as low as point three microns. This covers nearly everything that there is including cooking smoke, paint pigments, fungal spores, and so much more.
  • MERV Seventeen Through Twenty Filters – I mentioned that the above was the best it could get for home air conditioning. Well, that was correct. However, this MERV measurement of seventeen through twenty is the absolute best possible and is typically reserved for medical applications such as hospitals and doctor’s offices. These filters are known as HEPA filters and are rated to remove up to 99.97% of particles that are point three microns or larger. These cannot be used in a traditional home air conditioner though due to the increased strain the system would go through pushing air through the filter. In some cases HEPA filters can be used in the home but only after extensive modification to the HVAC system.

Now, after reading this you may wonder what the right filter is for you. In most cases I would recommend the MERV nine through twelve categories. This gives you a high quality filter and will provide you with clean air throughout your home. If you have a family member, or if you yourself, struggle with asthma or other allergies then you may consider the MERV thirteen through sixteen filters. In extreme cases a HEPA filter and system may be needed, but this can get quite expensive as you will have to get a non-traditional residential air conditioning system to support the HEPA filter.


Your air conditioner and your furnace are some of the most expensive appliances in your home. It only makes sense to take care of them and to ensure that they last as long as they can. In today’s world a new AC and furnace could cost anywhere between six to twelve-thousand dollars.

By ensuring that your air conditioner filter is taken care of every few months you not only protect your system and investment but it also provides you clean air throughout your home. If you aren’t already, please take the time to clean or replace air filters not only for your health but also for your wallet! If you’re looking for just the right filter check our Filter Purchasing Guide.