An Expert Guide to Air Purifiers

Air Filtration Expert Jeff C. gives a rundown of everything you need to know when shopping for an air purifier, and lists his top three in-home air purifiers!

Close up of an air purifier.

Photo by HS You

Introduction

It’s becoming more and more obvious that the particles that make up indoor air pollution are a health hazard. The buildup of contaminants such as dust, dust mites, pollen, smoke, mold spores, bacteria, pet dander, and other allergens are not only a problem for people with asthma and allergies but can also adversely affect healthy individuals over time. According to the Environmental Protection Agency (EPA), air quality indoors is likely to be two to five times more polluted than outdoor air. In some cases, the level of pollution indoors can be as much as 100 times higher. Air purifiers are designed to remedy this by removing these indoor contaminants. Even if you’ve never owned one, you’re probably familiar with air purifiers and have a basic understanding that air purifiers are designed to clean the air.

Air purifiers are different from the changeable filters that are found in your home heating, ventilation, and air conditioning (HVAC) system. Years ago, when you went to the hardware or home improvement store with the measurements for your unit, the salesperson would match you with a filter usually made from pleated paper or spun fiberglass. These filters would provide a very basic filtration. In recent years the manufacturers of home heating and cooling systems have acknowledged the need for additional filtration. Now there are special filters available for people bothered by allergies, filters with built-in activated carbon filters for the removal of odors, and much more. But studies have shown that this type of filtration is still not enough. For this reason, many families are looking to home air purifiers for a better filtration solution.

If you are looking into air purifiers, this article will give you the tools and knowledge to help to tackle the problems associated with improving your indoor air quality. I’m going to discuss a little about how air purifiers work, specifically how they remove harmful particulates from the air. I’ll also discuss some of the testing measures that are used to determine how well a purifier performs, including some independent non-bias testing programs. By the end, you’ll feel both knowledgeable and comfortable about shopping for an air purifier.

The Key to Efficiently Clean Air: Knowing Your Clean Air Delivery Rate

The basic principle for air purification, whether it is a tabletop unit or any other of the styles available, is basically the same. All units use fans to draw air into the purifier, then the air passes through a series of filters before clean air is distributed into the room. The rate at which this process happens is called the clean air delivery rate (or CADR). The clean air delivery rate is measured in cubic feet per minute (CFM). The higher the CADR number, the more air is passed through the unit each minute. So, one of the key numbers to keep in mind when shopping for an air purifier is the CADR rating.

Operating the air purifier at a higher fan speed increases the clean air delivery rate. Units that have air quality sensors will automatically detect the amount of pollutants in real-time and adjust fan speed according to the air quality and demands of the environment. The end goal is to provide four to five complete air changes every hour for the room or area that you are treating. With this in mind, you want to have a good idea of the size of that room by measuring its area in square feet. Multiplying the length by the width will give you the total square footage of the room. As an example, an average master bedroom is around 12ft x 14ft, which gives us a total of 240 sq ft.

So, how do we determine what clean air delivery rate is necessary to ensure we buy the correct purifier for the square footage of our room? For the sake of ease in explaining this, we’re going to go with the standard ceiling height of 8 ft as an example. Using the 8-ft ceiling model, the general rule is that the CADR of your purifier should be equal to two-thirds (⅔) of the room's square footage. So in our 12ft x 14ft example room, ⅔ of 240 is 145. This tells us that for our 240 sq ft master bedroom, we want to have a CADR that is at least 145.

Diagram of filter stages for the Winix A231.

Filter stages for the Winix A231

Pictured above is the Winix A231 and, according to the manufacturer, this unit has a CADR rating of 154 for pollen. Recalling that we wanted a minimum CADR of 145 for our hypothetical 240 sq ft master bedroom, when we compare the numbers, we see that this unit is capable of purifying the air in a room up to 240 sq ft with ease. Generally, manufacturers will err on the side of caution, and Winix states that the A231 is recommended for rooms up to 230 sq ft.

Where Does the CADR Rating Come From?

The clean air delivery rating comes from the Association of Home Appliance Manufacturers (AHAM). The AHAM is a voluntary certification program used by air purifier manufacturers to provide independent testing and feedback in the form of the CADR rating. The three areas tested are dust, pollen, and smoke. The reason for testing these three different pollutants is their particle size.

Particle size uses a measurement called the micron. One micron is 1/25000th of an inch. For comparison, a human hair measures around 50 microns. Dust is generally between 0.5 to 3 microns, pollen is 5 to 11 microns, and smoke is 0.09 to 1 micron. Quite often you will see CADR ratings with these three numbers because airflow and filtration efficiency rates are influenced by the size of the particle passing through the air purifier. There generally isn't a big difference between the three numbers, and if you calculate the average of all three you’ll get a solid base number for the purifier that you are researching. All modern air purifiers are designed to remove these three types of indoor pollutants and many others.

The Stages of Filtration

The Pre-Filter

The first stage of filtration is the pre-filter. The pre-filter is a larger mesh screen designed to trap larger particles like hair and lint. It is the first filter in the process of air purification. When shopping for a purifier, look for a unit where the pre-filter can be removed and washed. Keeping your pre-filter clean will help your air purifier run more efficiently, and it will preserve the life of the other filters.

HEPA Filters

All modern air purifiers on the market today contain high-efficiency particulate air filters or HEPA filters for short. I won’t spend a lot of time explaining how HEPA works, but you want to look for phrases like “true HEPA filter” and “medical-grade HEPA filtration” when researching the best protection for you and your family. HEPA air purifiers are responsible for removing the smallest particles from the air such as dust, mold, pollen, pet dander, bacteria, and viruses. The thing to remember when dealing with viruses is that even though HEPA air purifiers are capable of trapping and removing them, no company can guarantee that you will be 100% safe. While the goal is to remove these hazards, please remember that germs and viruses may be present in the room, possibly on surfaces, and are unable to be trapped by your high-efficiency particulate air filter. So while owning a purifier is better than not owning one, no one should claim that you will not catch a virus.

What About Odors and Gasses?

A woman drinks a cup of coffee by an open window.

Photo by Toa Heftiba

Odors and gasses are caused by volatile organic compounds (VOCs) and can be removed from the air by passing them through some type of activated carbon filter. Often called activated charcoal, it is heated during the manufacturing process to extremely high temperatures, then exposed to argon or nitrogen gas and reheated a second time. What this does is make the surface area of the charcoal more porous and thus more absorbent. The odors and gasses that pass through an activated carbon filter are trapped by those pores and removed from the air.

The Final Purification Stage

The two most common final stages of air purification involve the use of ionizers and/or UV light. Any particle small enough to make it through the HEPA filter is neutralized and destroyed at this stage. UV purification kills even the smallest particles and is also used in modern water treatment processes to keep drinking water safe. Ionizers, however, charge the air with electricity, and the electrical charge cleans the air.

One byproduct of ionizers is ozone, which is known to be hazardous to your health. For this reason, the Food and Drug Administration (FDA), the Environmental Protection Agency (EPA), the Occupational Safety and Health Administration (OSHA), and the National Institute of Occupational Safety and Health (NIOSH) have set limits on the amount of ozone a person should be exposed to. The strictest of these comes from the FDA and requires the ozone output of indoor medical devices to be no greater than 0.05 parts per million (ppm). For perspective, the amount of ppm that modern air purifiers generate is less ozone than is naturally occurring in outdoor air. Hopefully, this will ease any ozone fears.

My Three Favorites

Now I’d like to break down some of my favorite purifiers on the market. This short list includes a couple of straightforward options for you. But be assured that all are capable of providing great air purification. Just be sure to match the CADR with your room size. It’s my experience that quite often you get what you pay for, so for that reason, this list excludes any sub-par models with questionable components. I'll go through the pros and cons of each unit and give my take on overall performance.

1. Winix A231

The Winix A231 Air Purifier.

Let’s start out with the model that we used in our example above explaining CADR. The Winix A231 is classified as a tabletop model that is a great option for bedrooms and offices. It can be placed on a table or nightstand and it has all the high-tech purification capabilities of their larger units.

Key Features

  • AHAM Verified up to 230 ft2: The Wixix A231 is AHAM verified up to 230 sq ft, so you can be confident that you’ll be getting those four to five complete air changes in rooms of that size. If you’re thinking of giving this model a try in, say, a living room that is 1,000 sq ft, keep in mind that you’ll only get one complete room air change per hour.
  • An All-in-One-Filter: Another great feature is the all-in-one four-stage filter. It offers true HEPA and activated carbon all in one neat unit. This will make filter changing a breeze when the time comes.
  • Plasma Wave Technology: The A231 also has Plasma Wave technology that creates a wave of free radicals that destroys bacteria and viruses at the molecular level—just like its Winix big brothers. Helpfully, it does this without generating dangerous ozone.

What I like about the Winix A231 The Winix A231 would be a great unit for your first air purifier. It has a simple design, is super quiet at the lowest fan setting, and has all the powerful air cleaning technology of a larger unit. Its reasonable pricing also lets you try out home air purification without breaking the bank.

What I don’t like about the Winix A231 One of the main drawbacks is the limited square footage in which this unit can be used. Because it's rated at 230 sq ft CADR, it isn’t the best choice for areas like living rooms. You could use this unit in a large room but the complete air changes per hour drops from 5 to maybe 1.5. This is okay, but not optimal.

Remember the more air you move through the purifier, the cleaner your air will be, so when shopping for an air purifier, try to get as many complete air changes as possible per hour for the area being treated. For this reason, I would only use this unit in rooms smaller than 250 sq ft.

2. Molekule Air Mini+ Air Purifier

The Molekule Air Mini+ Air Purifier.

The second tabletop purifier I’d highly recommend is the Molekule Mini. This unit is very stylish and looks great in any room decor. It’s great for small rooms and includes a handy carry handle that allows you to move from room to room with ease. It is made with higher quality components than the Winix A231, however, both purifiers provide excellent purification. If Winix purifiers are like a Chevy, then consider Molekule air purifiers the Cadillac. Both will get you from point A to point B reliably and safely, but you look better behind the wheel of a Cadillac.

Key Features

  • Quiet Operation: This unit is “whisper quiet” and is made for even the lightest sleeper.
  • Air Quality Feedback: The real-time “air score” continually indicates the quality of the air. This is displayed from “Good” to “Very Bad” on the top of the unit. You can literally watch your air quality improve as the unit runs.
  • Automatic Air Quality Sensors: Another great feature is the automatic air quality sensors which adjust the unit's fan speed in real-time according to the values detected by the sensors. The unit uses a proprietary PECO filter system to destroy bacteria and viruses at a molecular level. Also, a real-time air quality mode lets you review the metrics via your smartphone with the Molekule app.
  • Apple HomeKit-Enabled: The Air Mini+ is also Apple HomeKit-enabled, so you can control it using the Home app on your iPad or iPhone. Just set it to “auto” and let it do its thing.

What I like about the Molekule Air Mini+ The thing that I really like about this filtration system is the Wi-Fi connectivity. Being able to connect and monitor your air quality in real-time is fun! Also, when it comes to style the Air Mini+ is an attractive-looking purifier. It blends nicely with most home decor, from modern to rustic.

What I don’t like about the Molekule Air Mini+

Just like the Winix above, the Molekule Air Mini+ is designed for small areas like bedrooms and offices, so you're limited on the area that this purifier will cover. If you want to cover a larger area, I would recommend the Molekule Air Pro.

The Molekule is also a bit on the pricier side and it’s considered on the high-end of tabletop models. That said, if you're like me and appreciate high-quality and cutting-edge style, the Air Mini+ is a solid investment for keeping your air clean and pure.

3. Rabbit Air A3 Artist Series

The Rabbit Air A3 Artist Series Air Purifier.

The Rabbit A3 is my all-time favorite air purifier. Pictured above is the Artist Series which offers multiple prints for customers to choose from. Rabbit releases new prints all the time, but The Great Wave off Kanagawa by artist Hokusai pictured here is my favorite print. Most recently they have introduced a Peanuts comic print that would be great for a child's playroom or bedroom. In addition to the prints, this model has all the bells and whistles that I listed with the other purifiers in this article.

Key Features

  • Multiple Filter Options: With the Rabbit A3 you can choose between four specialized filters (Germ Defense, Pet Allergy, Toxin Absorber, and Odor Remover). All the filters provide fresh, clean air, but each is uniquely designed to work harder to fight a specific type of pollutant. The nice thing is you can order the Germ Defense filter with the Rabbit A3, and when it’s time to replace it you can switch to Toxin Absorber. This allows you to experiment to find out which filter works best for you.

Expert Note: An Filtration and Air Purification Expert will explain the coverage area and be able to dial in the filter that best fits your current needs. Also, having a washable pre-filter will extend the life of any specialty filters.

  • Mobile App: It pairs easily with your mobile device, like a phone or tablet, and allows you to get a real-time snapshot of the quality of the air. Using your mobile device, you can also make adjustments to the purifier from anywhere. That way you know that your air will be fresh and clean when you arrive home, or you can give the room that extra boost before you arrive with company.
  • Wall Mountable: Other great features are the wall mount and the ability to hang the unit upside down because you can place it high on the wall and still access the control panel. In addition to the standard filtration found in most modern air purifiers, this one also has a laser technology particle sensor that will adjust fan speed in the auto mode based on the particulate in the air. You can view the particulate matter metrics in real-time in the app in three size ranges (PM1, PM2.5, and PM10). These numbers correspond to particle size in microns and is a pretty cool feature.

What I like about the Minus A3 This is my favorite purifier out on the market. I like how quiet it is, the ability to monitor the health of the room in real-time, and I like the style of the unit itself. It exceeds all my expectations for clean, fresh air and you also only need to buy a replacement filter once a year.

What I don’t like about the Minus A3 At its price, the Minus A3 is a serious investment, that said, I have no regrets about getting one for my home.

Conclusion

My goal in this article was to give you a few standout options, in the hope that you’ll find one that fits your needs and your budget—and I hope I’ve succeeded. Even with this knowledge, I’d still encourage you to get in touch with an Air Quality Expert to help guide you and answer any questions that you may have. Thanks for stopping by and may you and your family breathe easy!

Filtration & Air Quality Expert Jeff C.
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Jeff C.
Filtration & Air Quality Expert
Jeff here! How can I help?
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As a child of the '70's I've always been interested in clean air and water! This led me down a career path heavily focused on the environment! The whole science of taking contaminated air and water and making it safe to use again has been very rewarding. I'm still an active consultant with the Mojav...

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