How to Choose Air Filters to Reduce Indoor Air Pollution in Your Home

How can I determine how well the air conditioning system in my home is filtering the air, and how could I improve it to make it suitable for an asthmatic? -Reojo

Hi Reojo,

How good a job your central heating and cooling (HVAC) system does in cleaning the air in your home largely depends on the quality of the air filter used with it.

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

The Microparticle Performance Rating (MPR) measures only 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 are filtered.

To give you an idea of the size particles we are talking about, mold spores and pollen are usually in the 10-30 micron range, bacteria 2-3 micron, and tobacco smoke 0.5 micron. Here are some general guidelines to consider when choosing an air filter for your HVAC system:

  • MERV 1-4 Air Filters: These inexpensive fiberglass mesh filters only remove particles over 10 microns in size and do very little to improve the indoor air quality in your home.
  • MERV 5-8 Air Filters: Medium quality pleated air filters that can remove particles down to 3.0 microns in size.
  • MERV 9-12 Air Filters: High quality air filters that can remove particles down to 1.0 microns in size.
  • MERV 13-16 Air Filters: Highest quality in standard filters. Removes particles down to 0.3 microns.
  • MERV 17-20 Air Filters: Also known as HEPA air filters (High Energy Particulate Air). These 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 first.

There are a number of other things you can do to help clear the air in your home in addition to installing a quality air filter and changing it regularly, including:

  • Limiting or removing carpets and rugs.
  • Keeping pets outdoors.
  • Reducing Volatile Organic Compounds (VOCs) in your home.
  • Use quality vacuum cleaner equipped with a HEPA filter.
  • Install a room air purifier equipped with a HEPA filter.

In addition, certain houseplants can improve air quality including philodendron, peace lily, dracaena, and snake plant.


Further Information


  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.


Please enter your comment!
Please enter your name here