HEPA Air Purifiers

How it works:

A mechanical device (the air purifier) forces air by means of a fan through a HEPA (High Efficiency Particulate Air) filter which then traps the particulates in the filter. The HEPA filter actually becomes more efficient over time as it collects more particulates. Although, it will eventually become too full and will need to be changed. Some purifiers have filters that require change infrequently with some models having filters that need replacement only every 3-5 years. The HEPA air purifiers often have a pre-filter which traps the larger particulates and these also need to be routinely changed.

The efficiency of a HEPA filter
A HEPA filter can remove up to 99.97% (that is, only 3 out of every 10,000 particles will pass through the filter) of particles down to 0.3 microns.

While extremely efficient, HEPA filters require careful handling during installation to prevent damage, due to the fragile nature of the microfiber media.

Benefits

HEPA filters have been shown to contribute to the reduction of the pollutants that can cause irritation to asthma and allergy sufferers. Hospital studies have also shown that HEPA filtration units are very effective in removing airborne particles.* HEPA filters are effective in reducing airborne pet allergens. For those who are concerned about the ozone which the electrostatic (ionic) purifiers can generate, the HEPA air purifier is a perfectly good substitute.

The HEPA filter is also an important component now in many of the hybrid purifiers that employ a variety of the possible air purifying technologies. It is often joined with UV air purifiers because the UV will destroy bacteria and viruses that pass through the filter while the HEPA filter filters out the larger particulates.

Disadvantages

The HEPA air purifiers tend to be more noisy than the electrostatic air purifiers. The industry has been aware of this problem and many models now operate almost silently on the lower fan speeds.

* T.C. Boswell, P.C. Fox.  "Reduction in MRSA environmental contamination
with a portable HEPA-filtration unit." Journal of Hospital Infection (2006) 63, 47-54.