How HEPA Air Purifiers Work

High Efficiency Particulate Air filters, also known as HEPA filters, are some of the most efficient air purifying filters made. A true HEPA filter will remove 99.97 percent of particles down to 0.3 microns in size. Because of their high efficiency these types of filters can remove the smallest of allergens such as dust, pollen, animal dander, smoke, and even bacteria, viruses, and chemicals from the air.

So how does a HEPA filter attain this high percentage of efficiency? The answer lies in the design of the filter itself.

The fibers of most HEPA filters are normally made of fiberglass that is arranged in a random pattern. The fibers themselves are between 0.5 and 2.0 microns in diameter. The random weave leaves airspaces greater then 0.3 micrometers but the way it is designed allows it to capture much smaller particles. There are three mechanisms at work that stop even the smallest of particles, trapping them to the fibers.

The first mechanism is Interception; the particles pass within one radius of a fiber and stick to it as the air stream draws them through the filter.

The second mechanism is Impaction; this is the primary function by which larger particles become trapped. Because they have to follow the curvy contours of the randomly woven fibers they are forced to embed directly into a fiber. The tighter the weave and higher the air flow the better this effect works.

The third mechanism is Diffusion; this is an enhancing mechanism whereby gas molecules collide with the smallest of particles, impeding their progress through the filter which raises the chance that the particle will be stopped by one of the first two mechanisms.

A HEPA air purifier also requires a fan the move air across its filter surfaces at a specified rate to garner maximum filtration efficiency.

For home use manufacturers have created single room units that simply pull air in through the back of the unit, across the HEPA filter and clean air exits out through the front. For whole home air purification HEPA filtration can be installed into the homes HVAC system. As the systems fan pulls air through the return air system it is filtered before returning through the supply side of the system. For homes with allergy or asthma sufferers a whole home filtration system can provide the relief they are looking for.

Born in the 1940’s during the Manhattan Project and commercialized in the 1950’s HEPA filters have evolved over the years providing a highly efficient air purification filter that provide a variety of benefits wherever they are used.