HEPA Air Filters
What is a HEPA filter?
HEPA (High Efficiency Particulate Air) filtration material was invented by the US government during WWII to prevent radioactive particles from escaping from military and scientific labs. HEPA filters are made of boron silicate (a glass-like substance) microfibres that are formed into flat sheets in a process similar to paper making. The flat sheets of microfibers are typically pleated to increase surface area, and the pleats are separated by baffles to direct airflow into the filter. Airflow is usually provided by a fan that forces air through the HEPA filter. The microfibers create a substrate with tiny, microscopic pores that trap extremely fine particles, thus making HEPA filters very effective at removing particulate-type contaminants. In fact, HEPA is widely recognized by independent authorities as being the single most effective type of particulate filter available today. Many air purifiers that feature HEPA filters also feature other air purification technologies that enhance removal of other common non-particulate airborne contaminants.
It is important to realize that not all HEPA filters are created equally. Only filters designated "true HEPA" or "medical grade HEPA" can promise to deliver the results cited above. Consumers must be vigilant to purchase only products with this designation, as un-certified filters can have significantly poorer results.
HEPA filtration is used in a variety of critical filtration applications, including those in nuclear, electronic, aerospace, pharmaceutical, and medical fields. They are the only type of filters recommended by authorities such as the EPA and American Lung Association for use as in-home air purifiers.
What contaminants do HEPA filters remove?
HEPA filters are simple, mechanical filters that remove particles including dust, pollen, mold spores, and dust mites from the air. While HEPA filters do not remove chemical gases or vapors, they remove particles VERY effectively - medical grade or "true" HEPA will remove 99.97% of particles that are 0.3 microns or larger from the air.
Benefits of HEPA Filter Technology
- extremely effective particulate reduction (best in class)
- excellent allergen reduction (mold spores, pollen, dust mites, etc.)
- well regarded in scientific and medical communities for its effectiveness
- unquestioned reliability
- cost effective to purchase, maintain, and operate
Negatives of HEPA Filter Technology
- requires fan to provide airflow - fan creates background noise
- filters require periodic replacement
- not effective at removing non-particulate contaminants
What to Look for in a HEPA Filter
First and foremost, you should ensure that the HEPA filter that you select is a "true" or "medical grade" HEPA. Not all air purifiers that are advertised as HEPA filters are equally effective. Also, look at the surface area of the HEPA media in the filter. The greater the surface area, the longer the filter will last. This is a major shortfall of many of the basic, inexpensive HEPA filters sold in big box stores. At first glance the system may look inexpensive and to be good value, but the cost of replacement filters that need to be changed every 6-12 months will quickly eat up those savings. Chances are that the unit will also have a louder fan with less fan speed control options as well.
While HEPA is extremely effective at removing particulate contaminants, it is not the best choice for removing smoke, odors, and chemical contaminants. This is why the manufacturers of higher-end HEPA filters add secondary filtration with activated carbon. We highly recommend a combination air purifier that uses both HEPA and activated carbon for almost all general home air purification tasks. As with HEPA filters, look for a system that contains a large volume of carbon. Many air purifiers sold in big box stores simply do not contain enough activated carbon to be effective.
Fan noise problems are limited through the use of multi-speed settings that are available on most models. We recommend that you select a HEPA filter that has several fan speed options so you can turn the unit down to a very quiet setting at night when you sleep and can turn it up during the day to increase the air processing rate.