ABOUT HEPA FILTERS

We hear about HEPA filters all the time. HEPA (High Efficiency Particulate Arrestor) filters are designed to capture all the particles in the air. They are challenged with a gas that is know to be made up of particle in the .3-micron range. The efficiency of the air filter is determined by how many of these particles get through the filter.

Typically HEPA filters will be classed by their ability to capture these .3-micron particles. A HEPA filter rated at 99.97% will be able to capture all but 3 out of 1000 particles of the .3-micron particles size.  A 99.99 will capture all but 1 out of 1000 and a 99.999 will capture all but 1 out 10,000 particles.

It would be good at this point to make sure we understand just how big a .3-micron particle is. If you were to look at the diameter of a hair you would be looking at about 100 microns.  Split the hair 10 times and you're down to 10 microns.  Split one of these 10 times and you're down to 1-micron.  Split this 1-micron 4 times and one of these would be about .25 or about .3-microns.  The naked eye can see particles about 25 to 30 microns in size if there is plenty of light.

HEPA filters are used in hospital operating rooms, clean rooms were manufacturing processes are critical and in labs where health issues are a concern.

HEPA filters have a high initial resistance so would load down a typical heating and cooling (HVAC) system in a home. To have an efficient HEPA filtration system requires 3 stages of filters. First you would have a pre-filter (such as the Filters By-George), then an intermediate filter and then the HEPA filter. The second and third filters would have more resistance than the home system could stand.

It's really not necessary to have all this filtration especially considering all the expense involved. The Filters By-Georg will capture about 35% of the .3-micron particles and about 90% of the 3 micron particles. ASHRAE (American Society of Heating Refrigeration and Air condition Engineers) has done studies showing that if we could capture 60% of the 3 (not .3) micron particles we would have most of the particles that get to the lungs. The three micron particles and above are the ones that germs ride piggy back on and get to the lungs. Our nose and throat catch the larger particles (20 microns and larger).  Bace to HOME