How good are HEPA filters really?

If you are serious about improving indoor air quality, then really your choice is limited to only a few air cleaning technologies, electrostatic precipitators and HEPA filters being the most popular solutions.

Although there are better quality filters around nowadays, they all are based on HEPA filter technology, and actually still bear their name, Hyper HEPA and Ultra HEPA filters being some examples.

The filter is made of sub-micronic glass fibers in a thickness and texture very similar to blotter paper.
If you’ve done any reading about filters then you know that a true HEPA filter is guaranteed to filter out any particles of 0.3 micron and larger.

The following lists the sizes in micron for frequently encountered pollutants in the household:

• Viruses 0.003 - 0.05
• Tobacco smoke 0.01 - 1
• Cooking smoke 0.02 - 1
• Combustion gases 0.02 - 1
• Bacteria 0.35 - 10 (99% of bacteria are larger than 1 micron)
• Skin flakes 0.4 - 10
• Pet dander 0.5 - 100
• Dust mite debris 0.5 - 50
• Household dust 0.5 - 100
• Mold 2 - 20
• Coal dust 2 - 100
• Pollen 5 - 100
• Plant spores 6 - 100
• Lint 10 - 100
• Human hair 70 - 100

As you can see, the only things on this list that are not trapped by HEPA filters are smoke and viruses, but you have to bear in mind that 90% of airborne particles are smaller than 0.3 micron. These are known as “lung penetrating particles” and are the ones most dangerous to your health.

The good news though is that HEPA filters do filter particulates smaller than 0.3 micron, even as small as 0.01 micron, but the percentage that is actually filtered drops of quickly at that size.

Claims have been made that HEPA filters become more efficient as they trap more particulates in the filter, but others claim that a dirty filter will increase the frequency that previously trapped pollutants are reintroduced into the air.

Also, a dirty filter is a breeding ground for micro organisms in a humid environment, so the best policy is probably to replace your HEPA filters on schedule, or when the indicator light goes on.

Good quality HEPA filters, will provide you with excellent filtration, but if the filter does not properly fit in the frame, performance can be seriously degraded due to the bypassing of unfiltered air.
So beware of cheap units, the filter might be ok, but the way it fits in the housing might be very poor.

For more information on related products, please choose from the following:

HEPA Air Cleaners | Replacement Filters