Air filters and purifiers are often recommended for people who suffer from indoor allergies, but those allergic to dust mites should consider this: Dust mites and their fecal pellets do not stay airborne for very long. They are relatively “heavy” and settle on surfaces in as little as twenty minutes after being disturbed. Air cleaners might therefore be most useful during housecleaning activities, and/or in tandem with ventilation be it open windows or air conditioning. Dust mite covers are much more effective according to reviews from allergy sufferers.
There are several types of air purifiers designed to extract allergens from indoor air. Each accomplishes this task with a different technology, with varying degrees of success when it comes to dust mites and their waste pellets.
Adsorption filters such as those with activated carbon (charcoal) only remove gaseous particles, not dust mites or their allergens.
Negative ion filters (ionizers) send negative ions into the air, thereby reversing the polarity of small airborne particles, causing them to clump and settle out of the air. Yes, they just redistribute the dust, not remove it. Dust mites and their allergenic wastes settle quickly anyway.
Electrostatic precipitators draw air into the unit and administer an electrical charge. The charged particles are then attracted to collecting plates that have the opposite charge. This only removes airborne dust mites and fecal pellets.
Ozone generators purport to kill bacteria, viruses, dust mites, and other biological contaminants. Unfortunately, such claims are usually exaggerated since ozone itself can be toxic to people (definitely a lung irritant); and at levels below government standards ozone is completely ineffective against airborne particles and organisms. (See the online EPA report on air purifiers).
HEPA (High Efficiency Particulate Air) filters can be very effective at removing airborne dust mites and their fecal pellets, but the area affected is limited (as it is with other devices).
Laminar flow air cleaners (with HEPA filters) do offer some relief to sleeping asthmatics when the device is attached to the bed. It produces a thin layer of clean air in the breathing zone of a reclining or prostrate person.
Even air purifiers that employ HEPA filters vary in their quality. The best models have these qualities:
A pre-filter that catches the largest particles, preventing clogging of the HEPA filter.
A motor that actively draws air into the unit rather than passively receives airborne particles.
Bear these factors in mind when selecting the best value for your money:
You usually do get what you pay for with air purifiers. Smaller, less expensive models are often noisy, have smaller filters and restricted air flow.
Purchase the model that is most appropriate for the size of the room it will be used in.
Remember that proper maintenance of any air purifier is paramount to its ability to function properly. That means replacing the filters as frequently as recommended by the manufacturer.
When contemplating the purchase of an air purifier, you may encounter terms like “MERV” and “CADR.” It helps to know what they mean.
MERV stands for Minimum Efficiency Reporting Value and applies to non-HEPA filters. The scale ranges from one (low) to twenty (high). Interestingly, a MERV value of 7-13 is comparable to the efficiency of a true HEPA filter. HEPA filters are more expensive, and have more restricted air flow than their MERV counterparts.
CADR translates to Clean Air Delivery Rate, and usually applies to portable air purifiers. This equates to the equivalent of introducing clean air into a room. For example, a CADR of 180 for dust particles means that particle concentration is reduced to the same level as that of 180 cubic feet of clean air introduced every minute.
The bottom line is that air cleaning devices are, at best, a mere supplement to proper housecleaning and dust mite mattress and boxspring covers, at least in the bedroom.