8 Things Homeowners Should Know About HEPA Filters

Understand what these air filtration products can do to improve the air quality in your home.

By Glenda Taylor and Bob Vila | Updated Apr 29, 2021 11:46 AM

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6 Things Homeowners Should Know About HEPA Filters

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Few things are as important as the air we breathe. One of the most popular products available in the ongoing quest for cleaner air—especially for allergy sufferers—is the high-efficiency particulate air (HEPA) filter found in a number of air-cleaning products. If you’re considering buying an appliance with built-in HEPA filtration, keep reading to understand what these filters can (and can’t) do to help improve the air quality in your home as well as what you’ll want to look out for when buying a HEPA air purifier.

The Most Important Things Homeowners Should Know About HEPA Filters

HEPA Filters History

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1. Decades before they made their way into the home, HEPA filters first appeared in nuclear facilities and hospitals.

HEPA filters were designed in the 1940s to protect workers in nuclear facilities from breathing radiated airborne particles. By the 1960s, HEPA filters were being used in hospitals to help stop the spread of airborne germs and particulates, and soon after they began to appear in household appliances, including vacuum cleaners, air purifiers, and whole-house air-filtration systems. The Energy Star branch of the Environment Protection Agency (EPA) defines HEPA filters as being able to “remove more than 99 percent of all airborne pollutants 0.3 microns or larger.” A micron is a microscopic particle, less than 1/25,400 of an inch long.

2. Allergy sufferers can get some relief with HEPA filters.

For asthma and allergy sufferers, air filled with dust, pollen, and dander can lead to respiratory symptoms, such as sneezing, watery eyes, sore throats, and trouble breathing. Fortunately, the airborne particulates that trigger allergy symptoms are relatively large in size and are easily trapped by a HEPA filter. According to the EPA’s Guide to Air Cleaners in the Home, using HEPA air filters in portable air-purifiers and HVAC systems can help reduce allergy and asthma symptoms. Currently, however, the EPA has no formal recommendations for the use of HEPA filters in the home.

RELATED: Allergy-Proof Your Home in 7 Steps

HEPA Filters Won't Remove Every Particle

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3. However, these filters won’t remove every particle from your indoor air.

Because allergens enter the home through open doors and windows—a single drafty window can let in millions of airborne particulates—using HEPA filters can’t guarantee the removal of all allergens. In addition, HEPA filters can’t remove the risk of all inhalable pollutants, including:

  • Some viruses: At 0.1 to 000.4 microns, some viruses are small enough to pass right through HEPA filters. Others, however, depending on the size of their particles, may be too large to get through a HEPA filter.
  • Bacteria: Bacteria range in size from 0.2 to 1 micron, so most bacteria particulates will become trapped in a HEPA filter. As the bacteria die, however, they decompose and release endotoxins (toxic substances less than 0.4 microns), which are small enough to escape a HEPA filter.
  • Volatile organic compounds (VOCs): Common household items such as aerosol hair spray, upholstery cleaner, ammonia, and many others contain VOCs—toxic substances that can irritate eyes and respiratory passages, and even lead to cancer. The gasses from VOCs are smaller than 0.3 microns, so a HEPA filter won’t stop them.
  • Mold: Airborne mold spores range from 3 to 100 microns, so a HEPA filter will trap them. However, the presence of moisture, which is common in air purifier filters, can permit the spores to grow, spreading mold throughout the filter. Eventually, a moldy filter can release spores on the other side as air passes through. To reduce the risk of a filter becoming moldy, replace it at least as often as recommended by the manufacturer. Where mold is a recurrent problem, consider an air purifier with an antimicrobial pre-filter to trap and destroy mold spores before they can reach the HEPA filter.

RELATED: 7 Reasons Indoor Air Isn’t as Pure as You Think

4. Pay attention to the terminology on filters’ labels.

The Department of Energy (DOE) specifies HEPA filters used by DOE contractors must be able to remove 99.7 percent of airborne particles 0.3 microns and larger, but no federal or national regulations exist for the consumer industry. Manufacturers of high-quality HEPA filters voluntarily test and certify their filters to meet DOE standards, labeling them as either “Absolute HEPA” or “True HEPA.” Manufacturers whose filters do not meet DOE specifications are often labeled as “HEPA-type,” “HEPA-like,” or “HEPA-style.” While they may be good filters, they haven’t been tested and certified as meeting DOE standards for HEPA filters.

HEPA Filters Vacuum Cleaner

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5. You’ll find HEPA filters in some air purifiers, HVACs, and vacuum cleaners.

The three most common home appliances to make use of HEPA filters are whole-house filtration systems designed to treat entire HVAC systems, portable air purifiers, and vacuum cleaners. For homes with family members who suffer from asthma or allergies, using one or more of these appliances may be helpful in alleviating allergy symptoms.

  • HEPA air purifiers: Portable air purifiers reduce dust, dander, and other airborne contaminates by drawing air into the unit and then exhausting it back into the room through a HEPA filter. Most purifiers are designed to run continuously, and many contain additional filters to neutralize household smells, such as cooking odors and smoke.
  • Whole-house HEPA purifiers: Whole-house HEPA filtration units, such as the Lennox PureAir S System, work to remove allergens from the air, via the home’s HVAC system. They are more effective at removing airborne particles throughout the home than portable air purifiers, which treat the air in a single room.
  • HEPA vacuum cleaners: Dirt that tracks in on shoes or pet dander tends to settle on the floor or upholstery, only becoming airborne when someone crosses the room or sits on the sofa. If you already use HEPA filtration to purify the air in your home, it makes sense to use a top-rated vacuum fitted with HEPA filters as well. These vacuums are fitted with HEPA filters to collect and trap dust, dust mites, and particles from floors and furniture before they become airborne.
Here's What HEPA Filters Do for Indoor Air Quality

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6. HEPA filters require frequent replacement.

Because dense HEPA filters trap most of the particulates in the air, they tend to become clogged more quickly than traditional filters. While the recommended replacement rate varies from appliance to appliance and depends on how much air is being drawn through the filter (and how dirty the air is), you can expect to change HEPA filters at least twice as often as you would change non-HEPA filters. This can be expensive, as a replacement filter for a standard vacuum runs approximately $10, while a replacement filter for a HEPA vacuum runs around $50.

7. HEPA filters can be washed and reused (in some circumstances)

The ability to clean a HEPA filter saves money. While filters differ and some are difficult to clean without damaging them, users may be able to eke out an additional few months or longer by cleaning a HEPA filter.

The cleaning process will remove built-up dirt, dust, and pollens from the filter while minimizing damage to its delicate accordion folds. Rather than sticking a HEPA filter under a running faucet, which is almost guaranteed to damage the filter as the water pressure makes contact with the delicate folds, the best way to wash a HEPA filter is by submerging it.

  1. Fill a sink with hot water, and then stir in a couple of tablespoons of a mild laundry detergent.
  2. Slowly and carefully, submerge the HEPA filter in the water, allowing the cleaning solution to saturate the entire thing. Lift and re-submerge the filter a few times—this allows the water to run through the filter and wash away the dust and contaminants. The water will become dark and dirty as the pollutants leave the filter.
  3. Drain the water, fill the sink with clean water and do the same thing—submerge, lift, and re-submerge the filter. This allows the clean water to rinse away traces of detergent.
  4. Remove the filter and set it on an absorbent towel, which will wick away excess moisture.
  5. When the filter is dry, which may take 2-6 hours, depending on the thickness of the filter and humidity, put it back in the vacuum or air purifier.
HEPA Filters Air Purifier

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8. HEPA air purifiers can capture some COVID-19 particles

With the arrival of the novel coronavirus, COVID-19, medical researchers and scientists have been working on ways to reduce the airborne spread of the virus. According to the Centers for Disease Control (CDC), COVID-19 particles are about 0.1 microns in size. Normally, this would be too small for a HEPA filter to trap since the filter traps particles only as small as 0.3 microns in size.

Fortunately, COVID-19 particles don’t travel through the air alone—rather, they’re attached to tiny respiratory droplets that are exhaled when infected humans cough, talk, or sneeze. A HEPA filter will trap these larger, human-generated droplets and, in doing so, can trap COVID-19 particles as well.

In the quest to control COVID-19 and reduce airborne transmission rates, air purifiers fitted with HEPA filters may play a role when used in homes and public settings, such as waiting rooms. Users should not assume that an air purifier equipped with a HEPA filter will entirely protect them against becoming infected. However, in conjunction with other precautions, such as wearing masks, washing hands frequently, and social distancing, HEPA-fitted air purifiers may help reduce the risk of infection.

How to Set Up, Use, and Maintain an Air Purifier

Before buying an air purifier to help clean the air in a home, find out how to set it up and use it most effectively.

How to Set Up an Air Purifier

Air purifiers don’t come with a lot of complex features, so they’re relatively self-explanatory right out of the box. However, for the best results, take some time to ensure the new purifier is set up correctly.

  • Unwrap the filters: Although HEPA filters are made to get dirty, they usually arrive wrapped in plastic and come pre-inserted in the machine. Without looking inside the unit, one would not know the filter is not ready to start trapping pollutants. The upside is that the user is immediately aware of how the filter fits in the machine—so, just remove it, unwrap it, and put it back in the same spot.
  • Move it away from walls: A natural tendency is to position an air filter near a wall so it doesn’t interfere with the walk space in the room. However, this is a mistake and can result in the purifier not drawing in enough air to function effectively. Ensure that the machine is placed a minimum of 18 inches from walls, furniture, or any other item that could obstruct airflow.
  • Learn the controls: To save time and better understand how the machine works, become familiar with the controls and features before turning it on. Many air purifiers come with programmable timers and other features best utilized when the user understands how they work.
HEPA Filters How to Use an Air Purifier

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How to Use an Air Purifier

A couple of usage tips, will help users get the best air-cleaning results from an air purifier.

  • Keep it on: Air purifiers are designed to run throughout the day and night, and many will increase or decrease power as necessary, so there’s no need to turn them off and on. Some can be programmed to run at a high setting starting in the morning and then switch down to the lowest setting at night to minimize noise. At high speed, a purifier emits about 50 decibles—similar to a dishwasher running. The purifier emits around 40 decibels on the sleep setting, comparable to leaves rustling or a PC fan running.
  • Enable the dust sensor: If the air purifier comes with a dust sensor, the sensor monitors the presence and amount of airborne pollutants and will adjust the operating speed to suit. If contaminants are low, the machine will run on the lowest setting, and when pollutants increase, it will run on a higher setting to clean the air more quickly.
  • Use one purifier per room: Moving an air purifier back and forth between rooms helps a little, but it’s not as effective as using one consistently in the same room.

How to Maintain an Air Purifier

The part of an air purifier that requires the most attention and maintenance is the filter. Most purifiers come with more than one filter, including pre-filters that block odors and some VOCs. Other pre-filters block larger airborne particles to keep a HEPA filter from clogging as quickly.

Air purifiers are rated by the amount of air they circulate, known as the clean air delivery rate (CADR). Clogged filters will reduce the machine’s efficiency so they should be regularly inspected—once a month, cleaned (as described above), or replaced with new filters.

How to Get the Most Out of an Air Purifier

Users can optimize the effectiveness of a home air purifier by following some tips:

  • Close the windows: While it’s impossible to keep all outdoor pollutants from entering a home, less dust and pollen will blow in by keeping doors and windows closed.
  • Use a vacuum fitted with a HEPA filter: Dirt tracked into a home turns to dust, and a regular vacuum can recirculate some of that dust when vacuuming. By using a HEPA vacuum, less dust will become airborne, and the air purifier won’t need to work as hard to clean the air.
  • Supplement with a fan: Air purifiers have their own internal fans that draw air into the unit and expel clean, filtered air, but users can contribute to the air-cleaning process by placing a fan in the room to help circulate the air. In this way, the purifier has access to air from a larger area.
  • Aim the purifier toward the breathing area: This may be a sofa, a bed, or a crib, but for the best results, especially in rooms where allergy sufferers will be, direct the flow of clean air where it’s needed the most.
  • Set reminders for replacing filters: If the purifier manufacturer recommends replacing the filter every six months, mark that date on your wall or digital calendar to ensure you don’t miss it.

How to Test an Air Purifier

When the air purifier is working as intended, it will reduce the amount of pollutants in the room, but users may question if it’s working as well as it should. The following three steps will help determine if the purifier is doing its job.

  • Check airflow: The purifier’s fan function is essential to the air-cleaning process. Put a hand in front of the clean airflow vent on the front of the unit to see if air is coming out. If it isn’t, the fan may not be working.
  • Check the filter: A dirty filter may also cause reduced airflow. Replace or clean dirty filters.
  • Use an air quality monitor: It can be challenging to second-guess the efficiency of an air purifier, especially if it’s a few years old and you’re wondering if it’s working as well as it should be. An air quality monitor that tracks pollen, dust, and other allergen levels can help determine if the air purifier is working as well as it should. Some air quality monitors are smart, meaning they sync with a home’s Wi-Fi network and allow users to monitor air quality from a smart device.
HEPA Filters How to Clean an Air Purifier

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How to Clean an Air Purifier

In homes where clean air is essential, it’s critical to keep the air purifier clean. At least once a month, it’s a good idea to clean the unit, but before you start, anyone in the home who has allergies should leave the room because the cleaning process may release pollutants into the air.

  1. Unplug the air purifier before opening the cabinet.
  2. Wipe down the exterior cabinet with a clean damp rag.
  3. Fit a vacuum with the brush attachment and vacuum the back intake and front outtake vents to remove any dust that may have collected.
  4. Remove interior filters and then carefully vacuum the interior of the unit with a soft brush attachment.
  5. Wipe the inside of the unit with a clean, dry microfiber cloth or a clean dusting cloth to remove bits of dust the vacuum may have missed. Don’t use a wet cloth for this part because it can cause dust to smear and stick to the interior.
  6. Replace or wash dirty filters (if necessary) and reinstall.
  7. Avoid spraying cleaners in the air purifier.

Other Ways to Improve Indoor Air Quality

Air purifiers do a beneficial job of removing pollutants, but users should take additional steps to keep indoor air clean.

  • Replace HVAC return-air filters: Check and replace these filters at least once every three months. It’s counterproductive to run an air purifier round-the-clock but forget to change HVAC filters.
  • Switch to beeswax candles: Candles are an undeniable source of ambiance, but if they don’t burn clean, they’ll be putting soot and carbon particles in the air. Beeswax candles are cleaner options.
  • Launder curtains: Fabric curtains attract and trap dust and pollen, and every time they’re disturbed, they release some of the particulates back into the air. Launder curtains—or have them dry cleaned—at least once a year.
  • Go clutter-free: Stacks of newspapers, shelves of knickknacks, and other little-used items collect dust and will reintroduce it into the room at the first hint of a draft. Reducing clutter makes it easier to keep the home dust-free.
  • Skip the houseplants: In homes with allergy sufferers, avoid having houseplants. Natural plants are at risk for mold and fungus growth, and some produce pollen that irritates respiratory symptoms.
  • Install radon detectors: Air purifiers do not trap radon gas, so if the home is in a region known for radon contamination, install one or more radon detectors in the basement or lower level of the house to alert residents to potential radon gas.
HEPA Filters Air Purifier Buying Guide

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HEPA Air Purifier Buying Guide

Breathing contaminated air is a nuisance for many but can be a health hazard for those who suffer from asthma or allergies. According to a study published in the Journal of Asthma, when air purifiers were placed in homes with children who suffered from asthma symptoms, after just 12 weeks, they felt better and showed fewer signs of respiratory problems.

Not all air purifiers clean the air equally—some, such as those with HEPA filters—are more efficient than others, some are designed for large or small rooms—and others might actually be hazardous to health.

HEPA Air Purifier Features to Consider

Consider the following factors when shopping for a HEPA air purifier.

  • Look for “True HEPA”: While other filters may be good, only air purifiers labeled as “True HEPA” or “Absolute HEPA” are tested and certified to remove a maximum amount of airborne particles.
  • Insist on a pre-filter: HEPA filters, being extremely dense, are quickly clogged if the air purifier has no pre-filters to trap larger airborne particles, such as pet fur and dander. Pre-filters lengthen the useful life of HEPA filters, and they’re much cheaper to replace.
  • Consider a timer: A programmable timer allows the user to set a daily operating schedule that automatically turns the air purifier to sleep mode at bedtime and then turns it back up to full power during the day.
  • Opt for a sensor: Air purifiers with dust sensors will monitor the air quality and automatically turn the unit on full power when dust, pollens, or other particles are detected, and then reduce the speed when the quality of the air improves. This saves time and will work in conjunction with a sleep mode, so the unit only powers up to full capacity during daytime hours.
  • Avoid an ozone generator: Some HEPA air purifiers also feature ozone generators that claim to produce healthier air by activating negative ions to destroy harmful bacteria in the air. Ozone generators are banned in California and discouraged by many health experts, including the EPA, which has determined artificially boosted ozone levels may trigger respiratory symptoms.
  • Check the CADR: The higher an air purifier’s CADR, the more pollutants it will remove from the air in a set period. CADR ratings are figured in the cubic feet of air that cycle through the machine per minute. For example, if the purifier has a CADR of 180, it will process 180 square feet of air per minute. The higher the CADR number, the more efficient the air purifier. Purifiers with CADRs ranging from 60-119 are considered “fair,” 120-179 “good,” 180-240, “very good,” and those with CADR ratings above 240 are considered “excellent.”
  • Conserve energy: Air purifiers are not at the top of the list when it comes to energy guzzlers, but some are still more energy-efficient than others. To conserve the most energy, look for the Energy Star logo that indicates the unit may save up to 40 percent more electricity over competing units.
  • Don’t forget room size: When it comes to air purifiers, err on the side of choosing a larger capacity unit rather than hoping a smaller capacity unit will be adequate. Air purifiers are labeled by the size of the room (square footage) they are designed to treat.
  • Filter cost: HEPA filters are pricey, so check how much replacement filters cost before buying the unit and check the manufacturer’s suggested replacement period.

FAQ About HEPA Filters

Clean air is a goal of many, but airborne pollutants are virtually everywhere. For those looking to reduce allergens, dust, and other airborne contaminants in the home, a few questions are to be expected.

Do home HEPA filters work?

Yes, by using HEPA filters in both vacuums and air purifiers, the user can reduce the number of airborne allergens and pollutants in a home.

Which HEPA filter is best?

A HEPA filter labeled “True HEPA” or “Absolute HEPA” has been tested and meets the criteria for being highly efficient.

How much does a whole house HEPA filter cost?

A whole-house HEPA air purifier attaches to the main trunk of a home’s HVAC intake duct and filters out harmful pollutants every time the furnace or AC is operating. Replacement HEPA filters for this type of purifier are the most expensive and can run $50 to $110.

Is there any filter better than HEPA?

Currently, HEPA filters are considered the top filters for removing airborne particles, such as mold spores, dust, dander, and pollen. They don’t, however, remove odors and some types of VOCs. By purchasing a HEPA air purifier that contains additional filters, such as a carbon filter and a pre-filter, the unit will remove a maximum amount of airborne pollutants.

Final Thoughts

When used in both air purifiers and vacuums, HEPA filters offer the best shot at cleaning indoor air. Other steps, however, such as keeping windows closed, not having houseplants, and laundering draperies regularly, are also necessary for reducing the number of airborne pollutants in a home.