Air Purifier Filters

Filters are one of the more important factors that you need to consider when choosing an air purifier.


The most common air cleaning technology makes use of filters to clean the air. Air is drawn from the room with a fan and is forced through a filter, or several filters.  As the air passes through, particles are physically captured by the filter.

This method of cleaning is an example of mechanical filtration,  the best known of which is the HEPA filter.  HEPA filters are excellent at removing particles as small as 0.3 microns. They are effective at stopping pollutants such as mold spores and many bacteria and viruses in addition to larger particles such as dust.

However, HEPA filters do not remove odors, chemicals or gasses. For these pollutants the most common type of filter is an activated carbon filter.

Activated carbon filters use carbon-based materials with excellent absorbent characteristics. Also, the activated carbon can be combined with other materials such as zeolite, potassium iodide and active alumina to increase its effectiveness.

Another important filter to know about when choosing an air purifier is what is known as a pre-filter. This is a filter designed to remove larger particles before they pass through the HEPA and/or carbon filters. By removing large particles such as dust, lint and hair before they get to the HEPA filter, a pre-filter can greatly extend the life of of your filter and improve your air purifiers efficiency.

Pre-filtration is especially important with activated carbon filters which would otherwise have much of their absorbtion capacity used up to collect these larger particles causing it to become saturated much sooner.

Replacement frequency, cost of replacement filters and the quality and efficiency of the filter itself can all effect how well your air purifier performs. A well designed air filter must remove air pollutants without overly restricting the air flow.

HEPA filters are pleated to increase the total square footage of filtering area, which means more filtering capacity. These pleats must be uniform and properly spaced so as not to restrict too much air flow.

The material used is also important. Thin paper is considered more effective than some of the synthetic materials on the market. On the better grades of HEPA filters the delicate filtering material is housed in a way that protects the material from being easily damaged.

While premium HEPA filters do cost more, their efficiency and their life span before needing replacement can make them a better investment in the long run.

Electrostatic filtration is another filtering technology you may encounter when shopping for an air purifier. This method of air cleaning uses various methods to attract charged particles and remove them from the air. There are four forms of electronic air cleaning: electrostatic precipitator; media charged electrostatic filter; negative ionizer; and ozone units. Each of these four methods have pros and cons and will be covered elsewhere.

Knowing the types of air pollution you are concerned with can help you decide just which type or types of filtration to choose. If you are not sufferring from a severe condition you may find a less expensive air cleaner is just right. If you have severe allergies or asthma then a higher quality unit may be the better choice.

Knowing how air cleaning works and what types of filters are designed to handle different forms of pollution can make choosing the right unit much less difficult.