How to choose an air purifier: Everything we have learned from years of testing.

We all have a vague idea of what the ideal air purifier should be like. First and foremost, it should quickly and efficiently get rid of a wide range of airborne pollutants, from large dust particles to minuscule bacteria and viruses. It should be immensely powerful, but also ultra-compact and whisper-quiet. Functional, yet affordable. And, ideally, beautifully designed.

The problem is, the ideal air purifier simply does not exist. As with anything else in this world, something has to give. We know — we have tested plenty of these appliances over the years. Even some of the best air purifiers come with drawbacks, whether that’s a monstrous size, noisy fans or an eye-watering price.

So what should you be looking at when buying an air purifier? There is no single answer to this question. Choosing an air purifier will largely depend on your preferred outcomes, personal preferences and the space you intend to use it in. You may have to reach some sort of a compromise between price, design and functionality, and get to grips with complex-sounding specifications.

Sound scary? Do not worry. We are making use of our years of experience to help you choose the best air purifier for you. Step-by-step, we will arm you with all the necessary knowledge to get the best value for your hard-earned money. While no air purifier is perfect and the results are never guaranteed, we hope that this guide will help you get through this hay fever season relatively sniffle-free.

Price does not equal value

If there is one thing that we have learned from testing air purifiers is that high price does not equal better quality — and our experts wholeheartedly agree.

“While higher-end air purifiers often provide more features and greater efficiency for large spaces, a well-chosen budget-friendly model can still deliver excellent air quality,” Dr. John McKeon, CEO of Allergy Standards, an international certification body for domestic appliances, and a principal at the Indoor Air Innovation & Research Institute, told Live Science by email.

What determines the value of an air purifier is the combination of its purification power (how much air it can clean per unit of time), its filtration technology and whether it is certified by reputable third-party organizations. Even some of the most affordable models meet these three conditions, McKeon said. “Indeed, higher-end purifiers often include air quality sensors, auto mode, mobile app connectivity and other frills, but while convenient, these features are not essential for effective air cleaning,” he emphasized.

That said, air purifiers that are efficient at filtering the air in challenging environments — in very large or extremely polluted spaces, for example — tend to be more expensive, McKeon said.

Understand the key specs

So, how do you find the purification power of an air purifier? Understanding the basic terminology will give you the upper hand here. Most models make claims of unparalleled performance, but knowing exactly how much air you want to purify will help you see through the marketing gimmicks and pick an appliance that suits your needs the most.

One of the most reliable ways to evaluate an air purifier’s effectiveness is by understanding its Clean Air Delivery Rate (CADR.) “This standardized rating, measured in cubic feet per minute (CFM), tells you how quickly an air purifier can clean the air in a given space,” McKeon said. Air purifiers with higher CADR ratings offer faster, more effective air filtration, while appliances with lower CADR ratings have lower purification power.

So what is the best CADR rating for your needs? “As a rule of thumb, the CADR should be at least two-thirds of the room’s square footage. For example, a 300-square-foot room requires a CADR of at least 200 CFM,” McKeon said.

Choosing an air purifier with the right CADR rating is particularly important for people with asthma and allergies to airborne particulates like pollen and pet dander. “Ensure the device can accommodate the size of the room it is being placed in or else it will not be as effective,” Melanie Carver, chief mission officer of the Asthma and Allergy Foundation of America (AAFA), told Live Science by email.

However, a higher CADR rating does not automatically mean better performance. “More expensive purifiers often have higher CADR ratings, making them better suited for large rooms. However, in a smaller space, a well-matched budget model with an appropriate CADR can perform just as well,” McKeon explained.

This brings us to another important specification — the coverage. This refers to the maximum square footage an air purifier is intended for, making it easy for the user to determine if an appliance can be used in their home. However, you should take this metric with a pinch of salt. Most brands will try to inflate the perceived performance of their products by stating the coverage that applies to just one Air Change per Hour (ACH), whereas “to effectively remove airborne triggers, you need at least 4 air changes per hour,” McKeon said.

You can calculate how many cubic feet of air an air purifier can clean per hour by taking into account the room’s volume (square footage x ceiling height) and the air purifier’s CADR rating, McKeon said. Multiply the CFM value by 60, then divide it by the room volume in cubic feet. If you want to see how many cubic feet of air it can purify within the recommended 15 minutes, multiply the CFM value by 15.

If maths is not your forte, find one of the online ACH calculators that can do these equations for you!

Pick the right air filters

Choosing the right filtration technology is another vital aspect when buying an air purifier. That is because it will largely determine the type and amount of pollutants that can be removed from the air.

Almost all of the best air purifiers for allergies work by trapping particles in air filters made of a porous, solid material like plastic or fiberglass. Other appliances work by passing air through an ionizer or electrostatic filter, which gives particles an electrostatic charge that causes them either to stick to metal plates or clump together and fall to the ground, Carver said. Certain air purifiers even combine several different filtration technologies. So which one should you choose?

Our experts agree that a True HEPA (High-Efficiency Particulate Air) filter is one of the most effective. “This filter can capture over 99.9% of airborne particles as small as 0.3 microns, including common allergens like pollen, mold spores, dust mites, and pet dander, making it a crucial feature for those with asthma and allergies,” McKeon said. “While premium models may offer additional filtration stages (an activated carbon filter for reducing odors, for example), a budget-friendly unit with a certified True HEPA filter can still be highly effective for smaller spaces,” he explained.

However, it is important to note that HEPA filters alone do not guarantee effectiveness. “For example, if there is a HEPA filter in an air cleaner but the seal around it is not tight enough, the air might be able to bypass the filter,” Carver said. This is why certifications from reputable organizations are so essential here — they do not just look at the filter used but how the whole appliance functions, she said. More on that later.

HEPA filters are a must, but what about other types of air filters? Whether you need them or not will largely depend on your needs and preferences. For example, many air purifiers are equipped with pre-filters designed to catch larger particles, such as dust or hair strands. In our experience, pre-filters can be very useful if you have pets, fluffy carpets or heavily soiled areas. However, we would not consider them essential.

Some appliances also include activated carbon filters. These thin layers of charcoal are designed to absorb odors and volatile organic compounds (VOCs), which are common household pollutants often characterized by strong, chemical smells. “Activated carbon filters may have benefits for people with asthma that is triggered by these irritants. However, these filters do not effectively trap allergens such as pollen or pet dander, which is why they are often combined with a HEPA filter,” Carver said.

Mind you, activated carbon filters are not a magic solution and they will never be a substitute for proper ventilation. Plus, they can differ in effectiveness between brands, if our experiences are anything to go by. Still, activated carbon filters can make a tangible difference to the air quality in your home, especially if you have pets, cook often or use a lot of cleaning solutions or paints in your home.

Finally, a handful of air purifiers are also equipped with ionizers. This feature may not be suitable for everyone, Carver told Live Science.

“While ion generators may remove small particles (e.g, those in tobacco smoke) from the indoor air, they do not remove gases or odors and may be relatively ineffective in removing large particles such as pollen and house dust allergens,” she said. “Another thing to note is that certain ionizers may produce ozone as a by-product, and this air pollutant can be harmful to people with asthma. Always look for trusted certifications, such as the Asthma and Allergy Friendly Certification Mark, to ensure there are no ozone emissions,” Carver said.

Look for independent certifications

Third-party certifications validate claims made by an appliance’s manufacturer and ensure it meets rigorous safety standards. They can help consumers make a more informed and science-backed decision when selecting an air purifier, our experts said. We thoroughly agree. With so many different models available on the market, it is difficult to know if something is truly worth the investment — having that endorsement can help you make the best choice possible.

“Look for certifications like the Asthma & Allergy Friendly Certification Mark, which verifies a high level of allergen removal efficiency and safety against harmful emissions like ozone. This certification ensures that the air purifier has been independently tested and proven to remove over 90% of allergens from the air, not just redistribute them. These products are also assessed for safety, including ozone emissions,” McKeon said.

Carved agreed and added: “The Asthma and Allergy Foundation of America (AAFA) joined with Allergy Standards Limited to develop strict standards for product certification. The Asthma & Allergy Friendly Certification mark on an air purifier ensures it meets AAFA’s high standards,” Carver said.

Other independent certifications to look for include Energy Star (this means that an air purifier meets strict EPA energy efficiency guidelines), UL 2998 (this ensures that an air purifier does not emit ozone) and CARB (this means that an air purifier has been approved by the state of California’s regulatory air quality agency, which is one of the strictest in the U.S.)

Pick the right design

We have talked a lot about the purifier’s performance, and rightfully so, but we can’t dismiss the importance of design. Factors such as size, looks, noise levels or controls can make or break your experience with an air purifier, regardless of its ability to filter airborne pollutants. Trust us here — we have downgraded plenty of appliances based on how much of a nuisance they turned out to be in day-to-day life.

When selecting an air purifier, take into account its intended placement to make sure it will not obstruct your living space or create tripping hazards. This is especially important if you have small children or overly curious pets. Also, make sure your air purifier is light enough if you intend to move it around the house a lot. It can be a real hassle, if not downright dangerous, having to lug a big, chunky machine from room to room.

Noise levels are another important factor to consider, particularly if you want to place your air purifier in a study or bedroom. Most appliances make around 40 to 60 dB (depending on the fan speed), which is comparable to a quiet conversation and, for most people, this is not particularly disruptive. However, some air purifiers (especially bigger, more powerful appliances at the cheaper end of the spectrum) can easily make as much as 80 dB when they kick into high fan speeds. That is equivalent to a noise made by blenders or hoovers, and not something that is easy to bear on a regular basis.

Feature-wise, we would recommend investing in an air purifier that has a built-in air quality monitor and an auto mode. Many, if not most, airborne pollutants are invisible to the naked eye, so it is not always obvious if your air quality has worsened. Similarly, it may not always be easy to tell if your indoor air is pristine and you may end up running your device at an unnecessarily high fan speed and wasting electricity for no reason. An air purifier with an air quality monitor and an auto mode can tell you how polluted your air is and adjust the fan speed accordingly. This way, you do not even have to think about it and you can just leave it to do its job. It is an excellent time-saver.

Consider the maintenance costs

The initial investment of buying an air purifier is not the only cost you will incur. First, you will need to account for the price of energy to run the appliance. It is tricky to quantify exactly how much you will pay as it differs from model to model and it will largely depend on your usage. If you are on a tight budget, you may want to consider buying an air purifier that is Energy Star-certified. While it may cost more to start with, it can save you money over time.

Secondly, air filters have a limited lifespan and the replacements can be surprisingly expensive. Most air filters last between six to nine months before they need to be replaced, but this can change depending on your usage and the level of air pollution you want to tackle. If you do now want to be up for a nasty surprise, check the price and expected lifespan of its replacement filters before committing to a specific appliance.

Lastly, check the warranty. In our experience, air purifiers do not break down that often. However, it is good to have peace of mind in case that happens.

This article is for informational purposes only and is not meant to offer medical advice.