Updated by Molekule staff on 5/25/2023
Choosing the best HEPA air purifier for allergies is no simple task, as the market is full of a great deal of variety. Different brands use diverse technologies stacked with the HEPA filter to complement its efficacy. Many models tout their ability to remove allergens from the air, but allergens can be as large as the grainy yellow pollen that covers our cars or as fine as smoke particles that get deep into our lungs and into our blood.
Molekule announced our PECO-HEPA Tri-Power last year, so let’s look at how HEPA air purifiers might work against allergens in the air like pollen, mold and others, and what that means for any allergies that affect you or your family. By the end of the article you will know what to look for in a HEPA air purifier and what features may be unnecessary and costly.
Common HEPA and allergy terminology
High-Efficiency Particulate Air filters, commonly known as HEPA filters, were first developed in the 1940s and are perhaps one of the most well-known commercially available technologies for purifying air. They are used in many different areas of daily life, including in aircraft, cars, and vacuum cleaners, as well as both commercial and residential air purifiers. The HEPA filter is a common standard in facilities where scrubbing pollutants from the air is vital, such as medical facilities like hospitals, or laboratories that deal with infectious viruses or radioactive material. Many allergy sufferers are advised to use HEPA filters to remove the allergens from the air that trigger allergy symptoms.
There are many terms associated with HEPA filters that you may encounter on your search for an air purifier. A basic understanding of these terms will provide a solid foundation of knowledge to build on as you assess how well a device will work on your allergies. There is a specific industry test that air filters must undergo, and if the measurements are within a certain range the filter can qualify as HEPA. If comparing a HEPA filter from one manufacturer against another, one will likely be better but both will meet the minimum HEPA requirements.
True HEPA: The basic measurement that HEPA filters need to satisfy is removal of 99.97% of particles that are 0.3 microns or bigger from the air. For the most part, if a manufacturer labels their unit to contain a “HEPA filter” with no qualifiers such as “HEPA-type” or “HEPA-like,” it should meet this standard, though you should check the percentage and particle size is indeed 99.97% at 0.3 microns.
For further verification with HEPA air purifiers, look for names of the organizations that publish the testing protocols: IEST, the Institute of Environmental Sciences and Technology, or ASHRAE, The American Society of Heating, Refrigeration, and Air Conditioning Engineers. ASTM, the American Society for Testing and Materials publishes testing methods for HEPA vacuum cleaners. Molekule uses a combination, the IEST method of measurement but the ASHRAE test pollutant (fine potassium salt). Our R&D team determined that because the salt is harder to capture it makes for a more accurate test.
HEPA-like or HEPA-type: A filter which may use similar materials and processes as a true HEPA filter, but may be of varying quality and a lower filtration efficiency standard. This term is not an industry standard. Look for an efficiency rate to know how it compares to HEPA, and if one is not available assume the filter won’t capture as many fine particles (the most dangerous particles) as a HEPA filter.
Allergen: Any substance that is able to cause an allergic reaction. Well-known allergens are dust, mold, pollen, pet dander and dust mite droppings, but rarer allergies can include chemicals in perfumes, from industrial manufacturing, or almost any other source. This article will focus on allergens that are particles and not gasses that cause allergies like artificial fragrances, as a HEPA filter alone cannot deal with gasses. A carbon filter, a PECO filter, or some other method of removing volatile organic compounds is necessary to deal with gasses.
How does a HEPA air purifier work to capture allergens?
The most common allergens are actually tiny proteins that come from living matter, whether from cat and dog dander, dust mites and cockroaches, plant pollen or mold. Allergen-carrying particles vary in size and composition, but allergens like pollen and mold spores can break into fragments smaller than 0.2 microns, making some added features within HEPA air purifiers more effective than others.
There are four key ways listed below that HEPA filters capture these allergens, but the main thing to remember is that they are captured on the filter surface:
- Sieving is the process by which particles too large to pass between the extraordinarily small distance separating HEPA fibers become entangled in one or more fibers. This only occurs with particles that are large compared to the fibers.
- Impaction and interception occur when smaller particles collide with a filter fiber and the air passing through the filter is insufficient to move them. Impacted particles strike the surface of the fiber and make a tiny impact crater they cannot escape from. Intercepted particles chemically or physically stick to the surface of a fiber.
- Diffusion is when very tiny particles are buffeted by the air currents in the filter and cannot escape before becoming impacted or intercepted.
The 0.3 micron particle size is used for testing because it is the size of a particle most likely to penetrate a HEPA filter by being too small to be sieved and too large to be subject to diffusion. Particles of this specific size are effectively a HEPA filter’s weakness. If a filter can capture a particle of this size, it follows that it can capture particles of most other sizes as well.
After capture by one of these mechanisms, particles like pollen or mold spores can dry and fragment into smaller bits that are then captured by a different mechanism. Note that HEPA traps allergens on a filter surface, and does not permanently remove them. PECO-HEPA filters are designed to destroy allergens.
Other considerations
In order for any of these processes to work correctly, the HEPA filter needs to be functioning properly and moving a large enough volume of air through clean filters.
To determine the efficacy with which an air purifier cleans the air, the market created a standard called the Clean Air Delivery Rate (CADR). CADR is typically shown as three numbers for pollen, dust, and smoke, and technically describes the amount of air, per minute, that will be cleaned of those particles. Unfortunately, this figure mainly speaks to how fast the air is moving through the filter, and not necessarily how clean the air is. Note that the substances that cause the allergic reaction – the actual allergens – are tiny chemical components of the particles trapped by the filter, and are not part of the equation. However, CADR can be a good starting point when assessing the potential performance of a HEPA air purifier.
It is also very important to take care when handling a HEPA filter and be sure that manufacturing guidelines are adhered to. It requires a lot of power to force air through the dense maze of HEPA fibers, so it must be well-sealed into the purifier. If there is even the smallest hole, the dirty air will seek out the path of least resistance which is right through that hole.
Different types and features of HEPA air purifiers
Standard HEPA only
While rare, these are HEPA air purifiers that contain the standard “true-HEPA” filters (99.97% efficiency at 0.3 microns particle size) without other added technologies in the unit. Almost all HEPA filters on the market today are paired with a carbon or charcoal filter to remove gasses. HEPA filters work on allergens as discussed above, where the mesh of fibers undergo impaction, diffusion, sieving and interception to capture pollutants from air passing through.
Electrostatic HEPA
Some HEPA filters have electrostatically charged filters, which means the fibers were manufactured to carry a static charge during operation. Some pollutants are attracted to the charge so this addition increases the efficiency of the interception mechanism.
HEPA with UV-C
UV-C is a specific type of ultraviolet light which has mutagenic properties that help HEPA filters by sterilizing biological contaminants that are trapped on the filter. The light eliminates germs by disrupting their DNA and renders them unable to reproduce. Otherwise microbes can feed on the trapped dirt in the filter and multiply, eventually overwhelming the filter and riding the air currents back into the room.
HEPA with carbon filter
The combination of a HEPA filter and an activated carbon filter is seen in most commercially available units. Carbon filters have the ability to grab many airborne chemicals from the air such as volatile organic compounds (VOCs), ozone, and other toxins. This approach uses both the physical particle removal of HEPA and the adsorption capabilities of carbon. Some HEPA filters have carbon on their fibers, but many air purification devices place a carbon bed inside the unit separate from the HEPA filter to capture what the HEPA cannot.
HEPA with PECO
Molekule’s PECO-HEPA Tri-Power filter uses both activated carbon and our proprietary PECO technology with a HEPA filter. The HEPA component traps particles and the carbon traps gasses, then the PECO catalyst adds another layer of protection by destroying allergens, mold, viruses, bacteria, chemicals, and more.
HEPA with metal oxide catalyst
A catalyst is a substance that can speed up a chemical reaction without itself being used up in that reaction. Air purifiers featuring a metal oxide (usually titanium dioxide) catalyst react with pollutants to vaporize or otherwise decompose them to their component parts. This is a separate mechanism inside a purifier and is usually placed after the HEPA in the flow of air through the device. Some of these devices may not completely catalyze pollutants, so it’s a good idea to check the device is both ozone-free and does not produce byproducts.
HEPA with ionizer technology
Ionization changes the charge of particles in the air, which makes them attracted to opposite charges. Some ionizers are designed to charge particles then release them back into the room so they can stick to the walls and floor. This isn’t a great solution not just because they can be stirred up by foot traffic again, but because they stick to your lungs better, too. Finally, the pollutant ozone is charged and may be formed along with the other charged particles.
However, when used with a HEPA filter, ionization can increase the efficiency of the filter because the charged particles stick to the fibers better. If selecting a device with an ionizer, be sure it is ozone-free and the charged particles are blown directly into the filter, not spread around the room.
HEPA imitators
“HEPA-like” filters that may be conceptually similar to true HEPA, but don’t necessarily achieve the same levels of efficiency as true HEPA. The quality of these filters aren’t guaranteed to match HEPA filters as they are not certified to true HEPA standards.
Best types of HEPA air purifier for allergies
Dust, mold, bacteria and pet dander are some of the most common allergens present in our air. In general, they can be removed to a high degree of efficiency (99.97%) by true HEPA filters, though efficiency could be affected by type of allergen. Research has shown that for pet dander, standard HEPA filtration is especially beneficial, while less so on dust mite allergens.
The combination of HEPA and activated carbon might be a good solution for people with pets. Pet dander is captured by the HEPA and smells are removed by the carbon. Keep in mind that carbon filters can become saturated over time, and may need to be changed when in an environment with extra-potent smells or with excessive gaseous pollutants, such as during a wildfire.
Molekule’s PECO-HEPA Tri-Power filter was designed with allergies and asthma in mind. The HEPA filter can trap most particles that are carrying allergens while the carbon removes gasses that can irritate or trigger reactions. The final PECO layer then destroys chemicals like ozone and VOCs in addition to biological particles like viruses and allergens.
HEPA filters on their own are quite capable of dealing with dust and dust mites, a common cause of allergies, though filters cleaning a high volume of air, necessary for allergen removal, may be extremely noisy. Depending on the placement of the purifier, sound volume may become a major consideration, especially if used in bedrooms.
Choosing true HEPA filters paired with just a carbon filter eliminates the possibility of producing ozone as a byproduct of ionizers or UV-C add-ons. Additionally, it reduces the amount of power required to run the unit to some degree, as both ionization and UV light production are energy-consuming processes.
Worst types of HEPA air purifier for allergies
Most of the airborne pollutants that bear allergens are particles, which true HEPA filters excel in removing.
However, because there are “HEPA-like” filters, and other lower-grade filters made of cheaper materials, simply buying any unit on the market may not be an adequate allergy solution. Less efficient filters might be okay for large pollen grains or mold spores, but will fall down trying to capture fine particles like the fragments of pollen and mold.
Moreover, additional technologies often seen in conjunction with HEPA filters may not be necessary to combat the allergens that trigger allergies. Most important is to be sure the purifier does not produce ozone, which can potentially exacerbate allergy symptoms. The California Air Resources Board keeps a list of ozone-safe air purifiers.
Noise, energy, and ease of maintenance
Aside from the simple volume-per-hour air flow through the machine, there are a number of factors which one can use to determine the cost-effectiveness of air purifiers.
Usage
Does the unit need to move from room to room? If the answer is yes then it may be worth thinking of getting one that weighs little, or has a handle to facilitate ease of transport. Some HEPA filters are the size of small cars, whereas others are lightweight, portable, and aesthetically pleasing.
Noise Production
If the air purifier needs to run overnight in a bedroom, the noise it produces should be a serious consideration. Certain steps should be taken to ensure that the air purifier selected is quiet or that it can be remotely controlled or scheduled to clean the air during preferred periods.
A great convenience enjoyed by many is the ability to control their HEPA filters by their phone with an app like the Molekule app. When it’s time for bed or upon the arrival of guests, a simple application can quiet the machine down.
Some purifiers, such as Molekule Air Mini and Molekule Air Pro, can be set to automatically react to pollution by using onboard sensors. These purifiers can minimize noise when there isn’t an air quality issue.
Energy Consumption
The cost of having an air purifier is in part affected by the power it draws, which can be as little as a light bulb or considerably more like a heater. It is important to know exactly what the desired use of the unit is, as having a unit with additional features will mean a greater power consumption. The ability to schedule or fine-tune the operation of the filter will greatly affect power consumption, as you can ensure it runs when it’s most convenient. Like with noise, air purifiers that can automatically adjust to changing air quality conditions will be more efficient than manually adjusted models.
Maintenance
Maintenance is vital for all HEPA filter air purifiers to achieve consistently clean air. Replacing filters should be done regularly, and if filters seem clogged or the air isn’t as fresh they may need to be changed more often. Replacing filters on time is especially important with HEPA filters, to prevent any mold captured on the filter from multiplying.
Some air purifiers, like those with carbon activated sheets, require more frequent maintenance, whereas those featuring ionizer technology will need professional repair, usually back at its manufacturer and rarely for free. UV bulbs can generally be replaced easily, but since they contain toxic mercury vapor extreme care must be taken during replacement and disposal. Devices that use UV LEDs instead of bulbs don’t have this danger.
The best HEPA air purifier for allergies is…
… any purifier with a simple, straightforward true HEPA filter inside a unit. Of all the technologies, the true HEPA filter should be enough to remove particles with allergy triggers, though you should also consider the right combination of low power consumption, high CADR and acceptable noise level.
The unit should be quiet and portable enough to be convenient, yet effective enough to tackle allergens in the air. You can look for dB levels and weight listed on the package, though not all manufacturers list sound levels. The unit should be placed comfortably in bedrooms as well as living spaces and be simple enough to maintain, requiring easy filter replacements. Furthermore, an air purifier with simply a HEPA filter and without all the other technologies could be more cost effective. The price of an air purifier might increase accordingly with add-ons like carbon or UV technology, though the unit may or may not actually improve allergy conditions within the home. While preventative cleaning and other steps are necessary to ensure a minimal-allergen home, a true HEPA filter can help remove dust, pet dander, mold and other common allergens from the air.
