Everything You Need to Know
About HEPA Filters

By Beth Krietsch

Our living environments are filled with far more allergens and pollutants than we’d like. High-efficiency particulate air filters (HEPA for short) remove pollutants from the air and allow us to breathe easier. This type of air filter works by trapping and preventing small, potentially harmful particles like dust mites, dirt, smoke, dander, and pollen from getting into your home’s air ducts. HEPA filters collect and remove these pollutants by forcing the air to pass through a very fine, mesh-like web of fibers.

How HEPA filters work

HEPA filters trap contaminants in four different ways as they pass through the filter:

  1. Impaction—Contaminants stick to the fibers as they move through the filter.
  2. Interception—Occurs when a particle attempts to move through the air filter but hits and sticks to a fiber instead.
  3. Diffusion—Happens when particles are bounced around by gas molecules and eventually stick to one of the fibers.
  4. Sieving—The contaminant gets stuck between two fibers when passing through the filter.

You’ll see HEPA filters most frequently in home air purifiers and vacuum cleaners. To qualify as a HEPA filter, the filter must trap 99.97% of pollutants that measure 0.3 microns or larger in size. One strand of hair is about 100 microns in width—the filtered particles are very, very small.

A HEPA filter will not be able to trap gases, bacteria, viruses, or odors. Not all HEPA filters meet the US government standards—look for the terms “true HEPA” and “absolute HEPA,” which indicate that it does qualify.

How much does a HEPA filter cost?

HEPA filters vary in cost and range from $16–$95 depending on quality, estimated longevity, and manufacturer. Air purifiers that rely on HEPA filters range from $50–$1,000 depending on size, quality, and projected coverage area. HEPA air purifiers and HEPA filters can be purchased at most hardware, home goods, or big-box stores, as well as online.

How to choose a HEPA filter

To produce the cleanest air possible, HEPA filters and the air purifiers they’re used in must be matched to the space.

When buying an air purifier, make sure the HEPA filter has a clean air delivery rate (CADR) that meets the demands of your space. The CADR denotes how much air passes through the filter based on square footage, and some rooms may be too large for the filter to properly cleanse pollutants from the air. If the fit isn’t right, you won’t get the purification results you want or need.

Caring for your HEPA filter

HEPA filters have been called the gold standard in air purification. To care for your purification system or air conditioning unit, you’ll need to replace your filters regularly. Some will need to be changed out every three to six months, whereas others may last for one to two years. There are some manufacturers that make reusable filters.

If you’re seeking more information about how to change your air filters, you may wish to look up the manufacturer’s recommendations for your filter prior to cleaning or replacement.

The importance of HEPA filtration

Indoor air pollutants are one of the top five environmental health risks, according to the US Environmental Protection Agency (EPA). Fortunately, air filtration systems are one of the best ways to remove these allergens and other harmful materials that float throughout the air. Many HEPA filters are ENERGY STAR certified.

Purifiers that use HEPA filters are useful for asthma and allergy relief because they collect pollen, dust, and other allergens that would otherwise recirculate throughout a room.

People who suffer from dust or seasonal allergies may find relief by using purifiers with HEPA filters during times of the year when allergies are aggravated. Some purifiers have timers and can be set according to your needs.

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