Young woman opening vacuum cleaner with HEPA vacuum filter.

Let’s clear the air about something: There’s no quick answer to questions such as What kind of room air purifier should I buy? Do I really need to spend the money for a HEPA filter? What kind of vacuum should I get? And you don’t want a quick paid-for endorsement or implied seal of approval to do the thinking for you.

However, you can make informed decisions. Here’s advice from James Sublett, MD, a leading board-certified allergist and indoor air quality specialist:

Air Filter Basics

First, there is no such thing as an “air purifier” or as the name implies, an air filter that purifies the air. Some units fitted with a ultraviolet (UV) light kill viruses and bacteria but even this does not purify all the air you breathe. The best any air cleaner can do is remove small particles that pass through the filter.

The term HEPA (high efficiency particulate air) describes filters designed to capture 99.7 percent of all particles 0.3 microns or smaller (too small to see, but the perfect size to penetrate your lungs). This size covers all common allergens, from mold and animal dander to dust mites and pollen, along with some small particles from smoke and pollution.

HEPA filters are most commonly used in freestanding air cleaners and vacuum cleaners. If you see “HEPA-like” on the label, buyers beware. It could mean anything, but it is not a HEPA filtered unit.

Before You Buy

Reduce indoor air particles from the outside in. Replace old and energy-inefficient windows and caulk window frames to keep moisture, mold, pollen and insects from finding a way inside. Seal foundation cracks, insulate your home.

Inside, choose smooth surface flooring and furniture that is easily damp-mopped or dusted. Most particles that trigger allergy and asthma symptoms, like dust mites and mold spores, are airborne for a short time and then settle as dust. Homes with carpets are a reservoir of allergens; each time someone walks across or vacuums the carpet, particles fill the air.

Using a HEPA vacuum will trap some particles, leaving others that are stirred up into the breathing space to be removed by room or whole house air filtration.

Whole-House Systems

If you have a central HVAC system, consult with a reputable contractor about replacing the manufacturers’ filter with an approved (sized appropriately for your unit and the size of your air ducts) furnace filter with a Minimum Efficiency Rating Value (MERV) of 11 or 12 and then set the fan to run continuously. This will pull the air in your home through the filter and remove particles down to about 2 microns.

Remember to change the filter regularly, usually every 3 months. A whole house HEPA filter must be installed by a professional HVAC company and sized appropriately for your air handling unit, to protect the life of the equipment and to ensure air passes through and not around the HEPA filter.  Improperly sized air filtration systems can cause your unit to ice up or burn out and in some cases void the manufacturer’s warranty.

Some whole house air filtration units bring the fresh outdoor air inside and filter it before distributing it to the rest of the house. The point is, you have options that can be customized to your home.

Room Air Cleaners

For homes with no central HVAC, or if you have indoor pets, a HEPA room air cleaner may be beneficial. It is still important to take care of the settled dust reservoirs and keep pets out of the bedroom. The room air cleaner should be adequate to clean the air in the room where it is being used. Do not expect it to clean an entire home and remember – only the particles that pass through the air filter will be captured.

The appliance industry has established a Clean Air Delivery Rate (CADR) to allow consumers to match the appropriate room air cleaner to the room they want to treat.  Recently, laminar flow HEPA air cleaners have been introduced and may offer some benefit during sleep when used in special pillows.

Never buy ozone-generating “air purifiers.” According to the EPA and doctors, ozone is a respiratory irritant and may actually make your allergy or asthma symptoms worse.

Filters such as ULPAs (ultra-low penetration air) used in certain industrial or scientific settings or clean rooms are not suitable for the home environment. They are designed for closed settings where air is cleaned before entering the room, then vented out of the building. Normal family life with cooking, kids playing and pets doesn’t happen in sealed rooms, negating any additional benefit these filters may offer.

Remember: No air cleaner or filter can do it all. Cleaning up your indoor air is a multi-step process, and you first must go to the source of the allergen, whether it’s mold, dust mites, pets or critters. Air filtration is only one of several measures that may provide benefit to children and adults with allergies and asthma.