How to Choose Air Conditioner Filters

Danny Lipford shows the selection of air conditioner filters available for purchase
A quality pleated air conditioner filter, pictured at the left, will catch more particles than a cheap grocery store filter, pictured at the right.

How well your central heating and cooling system cleans the air largely depends on the quality of your air conditioner filters.

Filters are rated from 1 to 16 on the Minimum Efficiency Reporting Value scale. The MERV scale is based on the percentage of particles, from 0.3 to 10 microns in size, that the filter catches. The higher the MERV number, the better it filters the air.

The Microparticle Performance Rating measures very small particles between 0.3 and 1 microns. Ratings on the MPR scale range from 0-2200. The higher the number, the smaller the particles that a filter removes.

Mold spores and pollen are usually in the 10-30 micron range; bacteria, 2-3 micron; and tobacco smoke, 0.5 micron.

Understanding the MERV Scale

Here are some guidelines to consider when choosing air conditioner filters:

  • MERV 1-4 Air Filters: These inexpensive fiberglass mesh filters only remove particles over 10 microns in size. They do little to improve the indoor air quality in your home.
  • 5-8 Air Filters: These medium-quality pleated air filters can remove particles down to 3.0 microns in size.
  • 9-12 Air Filters: These high-quality air filters can remove particles down to 1.0 microns in size.
  • 13-16 Air Filters: These are the highest-quality, standard filters. They can remove particles down to 0.3 microns.
  • 17-20 Air Filters: These filters, also known as HEPA (High Energy Particulate Air) air filters surpass the standard MERV rating by removing 99.97% of airborne particles 0.3 micron and larger. While often used in hospitals, they cause too much air resistance to be installed in a standard HVAC system without making modifications.

Other Ways to Reduce Allergens

In addition to choosing quality air conditioner filters and changing them regularly, you can do other things to help clear the air in your home. 

Here are some examples: 

  • Limit or remove carpets and rugs.
  • Keep pets outdoors.
  • Reduce Volatile Organic Compounds in your home.
  • Use a quality vacuum cleaner equipped with a HEPA filter.
  • Install a room air purifier equipped with a HEPA filter.

Further, certain houseplants can improve air quality. These include philodendron, peace lily, dracaena and snake plant.


  1. I have been told by different A/c Tech’s that most A/C units can not have a Filter higher than a 9 Merv rating. If you go higher than 9 it will strain the unit on passing air flow and this will make the unit work harder and shorten the life of the unit.

  2. Had my ac air handler filter and blower acid wash by a professional ac company, but I still have no improvement on the air coming out of air duct. Still see some black stain up in the ceiling where the air from the air duck are coming out. My nose always itching and very bad allergies. Please advise, need help to what else can I do. I change filter from the wall every month.

  3. Should under house vents be left open in summer ? MY house feels cold under it but want to air out underneath. See some black mold on the lumber under house so wonder if not getting enough air to dry out. The mold is spots not heavy. My electric bills are low so dont think have air leak in ac ducts that run under house but never checked.

  4. We recently bought a home and had problems with the unit. The filters are needing to be changed about every 10 days. Our house is clean. No carpet, yes we have dogs and 2 cats. The repair man said this is normal because we live in the desert and have house pets. Our unit pipes ice up and struggles to cool until filter is changed.

  5. I was also told by my furnace/air conditioning installer to be very careful about how efficient the filter.It will strain the ac system. They suggested changing a less dense filter more often. If in doubt, call your installer and ask.

    • Totally, Deb. These are some base guidelines, but always check with your heating and cooling system’s manufacturer and read those filters carefully. Thanks for commenting!


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