Buying guide: how to choose an air purifier

There are many reasons why you may be considering purchasing an air purifier. You may be looking for an extra protection barrier to keep yourself and your loved ones safe from an epidemic such as the flu or COVID-19. You may also be suffering from allergies or asthma caused by pollen, dust and dust mites, and/or a pet that sheds. Another reason may be that you are living in a place with high levels of air pollution. Finally, perhaps you have a neighbour or family member who smokes and you’re looking to protect yourself from second-hand smoke.

Whatever the reason, equipping your home with an air purifier can bring a multitude of benefits to your health and wellbeing. The air purifying market is growing rapidly in Europe, and more and more individuals and professionals are equipping themselves with devices.  However, as a result of a market flooded with options, many people remain unclear about how to choose the right one. Read our guide below to choose the device that is right for you.

What is an air purifier?

An air purifier, simply, is a device that pulls in contaminated and/or polluted air, treats the air inside the device using a diversity of filters and technologies, and then circulates purified, pollutant-free air back into the room. Typically, you can find two types of filtration technologies within an air purifier: filters (such as a HEPA filter; these trap pollutants and impurities and must be changed when they become saturated) and depollution technologies (such as ionisation or active oxygen; these use active agents to depollute).

Not all air purifiers filter all types of pollutants. Some focus exclusively on biological pollutants such as allergens (dust and pet dander), for example. It is important to understand all the types of air pollution before purchasing an air purifier. Air pollution can generally be classified into three types:

Particulate pollution (PM)

What makes fine particle pollution particularly dangerous is that they are generally invisible to the naked eye, yet we inhale them all day long. They are commonly sourced from smoke, soot, pollen, and other allergens such as dust, and hair, to name a few. Certain activities performed in the home can create these fine particles, sometimes in large quantities, causing them to be suspended in the air. Some of these activities include DIY projects, cooking, cleaning, tobacco use, and burning candles. Fibres can also be a source of fine particles including those of both plant origin (cellulose, hemp, sisal, jute, etc.) and of mineral origin (asbestos, fibreglass, and mineral wool). Finally, lest we not forget a major culprit of fine particle production: heating with wood or the combustion of fossil fuels (and in particular exhaust gases).

Chemical pollution

This type of pollution is abundant, particularly in indoor settings. Some examples of chemical pollution may include carbon monoxide (also known as the ‘silent killer’: a colourless, odourless, and highly deadly gas that is released into our homes via poorly-maintained heating devices or devices used in confined spaces); volatile organic compounds (VOCs) (pollutants emitted by every-day products that we use at home including paints, solvents, furniture, DIY work, home furnishings such as new furniture, fragrances, and sanitising sprays); and semi-volatile organic compounds (VOSCs) (mainly found in materials used for maintenance of the home including coatings, wood treatments, pesticides and biocides, and flame retardants). Nitrogen oxides (NOx), sulphur dioxide (SO2), and pesticides (insecticides and fungicides) are also chemical pollutants.

Biological pollution

The last type of pollutants is sourced exclusively from living organisms such as animals, plants, or mould. There are three types of biological pollutants including infectious agents (bacteria, viruses, toxins), allergens (moulds, plants, animals, insects, and dust mites), and moisture (which leads directly to mould growth and can be found in poorly ventilated spaces).

Learn more about the different types of air pollution here.

Important note: an air purifier is not a dehumidifier or an A/C unit. It is not meant to regulate the temperature or humidity in the air. While some brands do offer 2-in-1 or 3-in-1 devices, the presence of humidity in an air purification device can be detrimental to the performance of its filters.

Consider the size of your space

Before choosing your air purifier, consider how much space you want your air purifier to clean. Air purifiers are sized based on the square footage of a room, meaning that by purchasing an air purifier that is too small, it may not properly filter all of the air in that space. On the other hand, if you purchase a device that is oversized for your room, it may be overkill and a waste of money.

A great way to determine whether your air purifier is properly sized is to look at its clean air delivery rate (CADR). CADR is a metric that was developed by the Association of Home Appliance Manufacturers (AHAM). AHAM is an independent association in the home appliance industry that verifies the energy, volume, and performance criteria of a wide variety of appliances, providing consumers with clarity and transparency on the efficiency of their products¹. CADR (in m3/hr), more specifically, is the airflow of the air purification device, meaning the volume of filtered air that it can deliver. The higher the CADR number for a specific pollutant, the faster a device filters out that pollutant. Air purifier models differ in that some may have only one CADR number whereas others may have multiple for specific pollutants (i.e. one CADR number for smoke and small particulates and another for chemical pollutants).

2/3 rule

According to AHAM, the rule of thumb when choosing an air purification device is to choose a device with a CADR number that equates to two-thirds of the room’s size. For example, let’s say that you are looking to purify the air in a room that measures 10 by 12 feet (3 by 3.6 metres), which has an area of 120 square feet (36 square metres). If dust is your main concern, for example, the CADR number of dust should be at least 80².

Consider the types of filter

Why is filter type important? Depending on the types of filter a device uses, it may or may not filter all types of pollution. You may be purchasing an air purifier for a specific issue, but if you are investing in an air purifier, doesn’t it make sense to purchase a device that does it all and rids your air of all pollutants?

HEPA filters

When researching air purifiers, one of the most important things you want to consider is the main type of filter with which your device is equipped. The most important designation for an air filter is “HEPA” (high efficiency particulate air). HEPA-certified filters are able to filter 99.97% of particles of a size greater than or equal to a diameter of 0.01 µm in a single pass. This means that all particles down to that size can be removed from your air: according to the chart above regarding particle size, that includes everything from coarse particles (pollen, pet dander) to the ultrafine particles that are particularly dangerous to our health. If you are looking to protect your lungs from allergens, germs, mould, smoke, volatile organic compounds (VOCs), and other harmful components found in polluted air, a HEPA-certified filter is a requirement.

There are different types of HEPA filters, which you can read more about here. We recommend HEPA H13 for most applications.

Buyer beware! There are many air filtration products on the market that advertise “HEPA-type” filters. These are filters that have not been tested for performance and cannot guarantee proper filtration of pollutants in your air.

Read more about HEPA H13 filters here.

Activated carbon filters

Some air purifiers come equipped with other types of filtration technologies such as activated carbon filters. Activated carbon is one of the most common filtration compounds in the industrial world, often used in both air and water filters to remove impurities. They can even be found in cigarette filters! It has a porous structure, allowing it to fix itself to pollution particles and gases. Activated carbon is extremely effective at filtering out chemical pollutants and VOCs. It is also known for its odour-fighting capacities, making it a desirable technology for those combatting cigarette smoke and other types of odours in their space.

Read more about activated carbon filters here.

Ionisation

Certain air purifiers come with ionisation capabilities. Eoleaf devices, for instance, are two-in-one devices, serving as both purifiers and ionisers. Ionisation is an effective method of controlling pollution because negative ions remove fine particles from the air. How is this done? Negative ions (negatively-charged ions, or “anions”), when released into your space, will use a phenomenon called ‘electrostatic attraction’ to attach themselves to fine particles (neutral or positively-charged ions) suspended in the air. Once attached to the fine particles, this will cause the fine particles to disintegrate entirely or to be weighed down to the ground. Your lungs and health are, as a result, protected from inhaling these dangerous particles.

Added bonus: having negative ions in our environment has also proved to bring a sense of well-being! This is done in several ways: 1) by promoting exchanges between cells with electrically charged membranes, 2) by encouraging the penetration of oxygen in the lungs (which, as you may remember from chemistry class, is negatively ionised), and 3) by stimulating enzyme action and neuromediator secretion (serotonin) and hormones (cortisol). Negative ions in our surroundings can have multiple benefits including reducing stress levels, improving concentration, and increasing our sleep quality. Natural settings such as waterfalls, the mountains, and the seaside contain high levels of negative ions, and ‘nature therapy’ is even being utilised in countries such as Japan and Finland for this very reason.

Eoleaf uses bipolar needle ionisation technology which does not emit harmful levels of ozone. Read more about ionisation here.

Photocatalysis

Another technology offered by some air purification devices is photocatalysis. What is it and how does it work? Photocatalysis can be found in a plethora of professional domains including the removal of pollutants and impurities from air and water. This process is also called photocatalytic degradation and is a chemical reaction accelerated by light (“photo” means “light”, and “catalysis” means “dissolution”). When chemical pollution is present in the air, free radicals released as a result of photocatalysis react with chemical compounds in the air and degrade them.

While photocatalysis is not a type of filtration, it is a particularly effective reaction that targets chemical pollution and gaseous pollutants like volatile organic compounds (VOCs). VOCs are linked to many household and industrial products such as solvents, cleaning agents, paint, cosmetic products, and new furniture, the latter of which may release VOCs for up to two years!

Eoleaf’s photocatalysis technology does not release any ozone. In fact, if there is ozone present in your space, the process of photocatalysis will destroy it and prevent the formation of new ozone by degrading its precursors (including oxides and other gases). Read more about photocatalysis here.

UV sterilisation

Finally, another technology offered by some air purifiers is ultraviolet (UV) sterilisation. A technology that has been used for over one hundred years, it is commonly found in hospital settings. How does UV sterilisation work? When UV radiation is absorbed by a microorganism, it disturbs its DNA, making it incapable of replicating (reproducing). This process ultimately leads to cell death and viral desactivation so these dangerous pathogens cannot spread⁵.

There are three types of UV light: UVA, UVB, and UVC. UVA and UVB both have longer wavelengths and are usually associated with sun damage (including skin cancer). They are the reasons why dermatologists advise us to wear sunscreen. UVC, on the other hand, has a short wavelength and the highest energy potential of the UV radiation spectrum; as a result, they have the most potential to combat pathogens. This is why UVC rays are the most common type of UV light used in air purifiers.

UV sterilisation does not sterilise the air because an air purifier’s airflow is much too fast to allow adequate exposure time. The amount of exposure time is crucial in determining the rate of pathogen inactivation or “killing”: studies show that 99.99% of airborne pathogens exposed to 40 mJ/cm2 of UV light at a wavelength of 254 nm, the wavelength typically used in air purifiers with UV sterilisation technology, will be inactivated or “killed”⁶. This technology is best paired with a HEPA-certified filter in order to reduce pathogen transmission, and it works against all types of pathogens, including bacteria, viruses, and microbes, regardless of their shape and size.  UV sterilisation is particularly useful because, contrary to other sterilisation technologies like antibiotics and hand sanitisers, it does not lead to bacterial resistance.

Read more about UV sterilisation here.

Consider how much noise an air purifier makes

Depending on where you plan to install your air purifier, it may be important to find an air purifier that is quiet but still powerful and effective (in a bedroom, for example). Be sure to check your prospective air purifier’s technical specifications to learn more about its noise level. To provide an example, Eoleaf’s AEROPRO 100, one of our more popular models, has the following noise levels:

• Speed 1: 30 dB (the level of a whisper)
• Speed 2: 41 dB (the level of average home noise)
• Speed 3: 51 dB (the level of faint rain)
• Speed 4: 62 dB (the level of normal conversation)
• Speed 5: 70 dB (the level of office noise)

Not all devices are like Eoleaf’s in that they can ensure you will never be disturbed at low speeds while remaining incredibly powerful.

Consider its maintenance costs

Air purifiers come with two costs: 1) the initial purchase of your air purifier and 2) its maintenance cost. This includes the electric consumption (read more on that in the following paragraph) and the cost of replacement filters. The initial cost of air purifiers varies greatly, as does the quality of the devices on the market and the depth/capability of their filtration. The same goes with air purifier replacement filters. Some replacement filters are cheap and must be changed often; others have very expensive filters that last for up to a year. Some filters can be washed; others are disposable.

Before making your purchase, make sure that your budget allows for the maintenance of the device. For example, Eoleaf’s devices require filter replacements only once a year in order to ensure proper functioning and continued filtration. Eoleaf’s air purifiers use an innovative multilayer technology where all the different types of filters are fused together in one piece.

Energy efficiency

Another characteristic to consider before making your purchase is how much energy your air purifier will consume. This, again, varies greatly depending upon the model and sizing of the air purifier. Intuitively, an air purifier sized for a small space will consume less energy. The opposite is also true: an air purifier sized for a large space will consume more energy. Air purifiers are most effective when left running on a nearly constant basis, meaning that your device has the potential to consume a high level of energy, especially if left running at its higher speeds.

Eoleaf air purifiers are remarkably energy efficient. Our devices even have an ECO standby mode when not in use, a setting that consumes less than 2W of energy. For example, the energy usage of our AEROPRO 40 model at its different speeds are as follows:

• Speed 1: 12 W
• Speed 2: 18 W
• Speed 3: 32 W
• Speed 4: 49 W
  

Air quality tracking

It is crucial to have a device that tracks air quality in real-time. This allows you to actually see how well it is working. Devices containing this feature usually have an automatic mode that will adjust the speed depending on the air pollution level at any given moment, making sure to protect you in the case of an influx of air pollution.

Extra features

Some models of air purifiers will come with additional features such as WiFi capability, mobile app integration, a remote control, filter-replacement indicator lights, wheels for easy portability, display dimming and shut off, and more. The presence of these features, again, will vary depending upon the air purifier.

Whether you need some or all of these features depends on your needs. Some of them will prove to be invaluable for your everyday usage, while others will fall in the “nice to have but rarely use it” category. But it’s nice to have the option! If you are looking for a device containing all of these features, look no further than Eoleaf air purifiers which come equipped with all of the above, allowing for a seamless, simple, modern air purification experience!

Once I’ve chosen my air purifier, where should I put it?

Choosing the correct location for your air purifier in your home or workplace can strongly impact its efficiency and performance. In fact, by correctly placing your air purifier, you can increase its efficiency by 20%³!

The two biggest things to keep in mind when placing your air purifier are: 1) where is the highest concentration of air pollutants in your space? and 2) where is the most air flow? For a more in depth guide, refer to our article on proper air purifier placement here.

Consider Eoleaf for your air purification needs

To answer any and all of your air purification-related questions, our dedicated, personal team of experts is here and happy to assist you in your quest to breathe clean air at home or at work. As we continue to face concerns with our air quality, it’s important to invest in a durable, high-quality air purifier that will stand the test of time and help you breathe better. Reach out today to find the best air purifier for your needs.

References

¹ Association of Home Appliance Manufacturers. (2019, July 22). About Aham. AHAM Verifide. Retrieved January 30, 2023, from https://ahamverifide.org/about-aham/

² Association of Home Appliance Manufacturers. (2022, March 23). Air Filtration Standards. AHAM Verifide. Retrieved January 30, 2023, from https://ahamverifide.org/ahams-air-filtration-standards/

³ Where to place Air Purifier? (7 golden 'best place' rules + bonus tip). LearnMetrics. (2022, July 5). Retrieved January 5, 2023, from https://learnmetrics.com/where-to-place-air-purifier/

⁴ Long, E. (2022, May 26). Buying an air purifier? here's what you need to know. Tom's Guide. Retrieved January 30, 2023, from https://www.tomsguide.com/reference/air-purifier-buying-guide

⁵ Beck, S. E., Rodriguez, R. A., Hawkins, M. A., Hargy, T. M., Larason, T. C., & Linden, K. G. (2015). Comparison of UV-induced inactivation and RNA damage in MS2 phage across the germicidal UV spectrum. Applied and Environmental Microbiology, 82(5), 1468–1474. https://journals.asm.org/doi/10.1128/AEM.02773-15

⁶ Center for Devices and Radiological Health. (2023). Ultraviolet (UV) radiation. U.S. Food and Drug Administration. Retrieved February 26, 2023, from https://www.fda.gov/radiation-emitting-products/tanning/ultraviolet-uv-radiation#3