Indoor Air Toxins 101: Do You Need an Air Filter?

which air filter

Wondering which air filter to buy — or if you need one? Here’s where to start.

Air-cleaning devices remove particles from the air. The easiest way to lower the concentration of particulates in your home is to vacuum and dust regularly. Air cleaners will remove suspended particulates while dusting will remove settled material that can become transiently airborne by shuffling papers, walking, etc. For those with chronic lung disease, such as asthma, a dose of dust that contains allergens can set off an asthmatic attack.

Air filters are the most common form of air cleaner. They may be placed inline with your home HVAC system, or on a free-standing air purifier unit where they remove particulates from the airstream passing through the filter. Air filters are rated according to a minimum efficiency reporting value (MERV) unit ranging from 1 to 20. The higher the rating, the smaller the particles that will be trapped by the air filter. The most commonly used air filters used in residential homes to fit inline with air conditioners and furnaces typically have a MERV value of 1 to 4. These filters protect the HVAC equipment from the buildup of unwanted materials on the surfaces of the system, but don’t improve indoor air quality. Pleated filters with a MERV value between 5 and 16 will remove both small and large airborne particles. Filters with MERV values over 7 are increasingly effective at removing particulates. Filters with a MERV value between 14 and 16 are almost as efficient as HEPA filters at absorbing PM2.5 particles, but may require increased fan and motor capacities if they are used with your home HVAC.

A true high-efficiency particulate arrestance (HEPA) filter is designated with a MERV value over 17. These filters will effectively remove PM2.5 particulates from your indoor air, but are not normally installed in residential HVAC systems, as they require modifications to the air- handling system. HEPA filters are more commonly available as portable units that can be moved from room to room. If your home is drafty and is located in a region with significant outdoor air pollution, consider that PM2.5 particles are being brought into your home daily, and invest in a HEPA filter. Removing PM2.5 particles from your indoor air will improve your health and longevity.

If you purchase a portable air cleaner, be aware that these machines are rated according to their clean air delivery rate (CADR), a measure of how much contaminant-free air is delivered in cubic feet per minute. Evaluating the CADR will help you determine what size room a given filter will function best in. Although portable units, especially those with HEPA filters, are effective at removing microparticles, most portable air cleaners are ineffective at removing large particles, such as pollen and dust mites, which settle quickly on surfaces. Vacuum cleaners fitted with HEPA filters will draw up both and trap microparticles, removing them from the environment.

Electronic air cleaners and ionizers use a different technology than air filters to remove airborne particulates. Air cleaners draw air through an ionization chamber in which particles accumulate a charge. The charged particles then aggregate on a series of oppositely charged flat plates called collectors. Similarly, ionizers emit charged ions into the air that adhere to airborne particles, giving them a charge. The charged particles attract each other and nearby surfaces, such as walls or furniture, and settle faster.

There is no standard measure to compare the effectiveness of electronic air filters. In general, ionizers and electronic air cleaners are not as effective at removing microparticles as filters are. In addition, they can create more indoor air pollutants by producing toxic ozone and ultra-fine particles (PM2.5) when reacting with VOCs from cleaning products, air fresheners, etc. For these reasons, I would not recommend investing in an electronic air cleaner.

Ultraviolet germicidal irradiation (UVGI) cleaners use UV lamps to destroy viruses, bacteria, allergens, and molds, which are all pathogens that can grow on HVAC surfaces such as ductwork, drain pans, and cooling coils. UVGI cleaners need to be used in combination with a filtration system.

Unless you live in an area with poor outdoor air quality, an HVAC inline pleated air filter with a MERV value between 5 and 14 should suffice for particulate removal. Remember to change the filter at least once every six months. Consider purchasing a portable HEPA air filter and keep it running in your bedroom or whichever living space you spend most of your time in. If you or your child has asthma, this will further help keep down the level of PM2.5 particles in the treated room. In addition, by vacuuming and dusting the home at least once a week with a vacuum fitted with a HEPA filter, the concentration of dust in home air will significantly diminish. Make sure to steer away from HEPA filters that masquerade as synthetic air fresheners—these actually release VOCs into the air as you vacuum.

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