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Generally a high efficiency filtration system will capture all the particles that go through it that the naked eye can see, plus a whole lot of the particles that can only be seen with a microscope. The High Density Media type filters will generally catch most all of the particles bigger than 10 microns in size. As the particles get smaller the efficiency gets lower. At about 1.0 microns the efficiency goes to about 40%. A micron is a very small particle (1 micron = 1/25,400 inch). A human hair is about 100 microns in diameter. House dust ranges from 0.01 microns to over 100 microns in size. Pollens and spores range from 10 microns up.
The biggest problem with filtration systems is that they only catch the particles that go through them. Most of the dust and particles that you can see would be considered very large, heavy particles. These particles do not stay airborne for very long. They have a tendency to fall out of the air stream quite rapidly and therefore deposit themselves on the flat surfaces in your home. Most of these particles never make it to the intake of your air conditioner and therefore your filter never has the opportunity to catch them. If your intake grille for your air conditioning unit is in the ceiling then it is even harder to get the large particles to stay airborne long enough to be drawn up into the system to be caught in the filter. So don’t expect any filtration device to eliminate the dust in your home or completely purify the air that you breathe. The higher efficiency filters will keep the air conditioning equipment cleaner which will make it operate better. I have seen systems that were installed with a high efficiency media type filter that have run for 15 years or more and the coils were still clean when they were changed out.
high efficiency air filter mesh