Alen FLEX Air Purifier Review: Quiet and Powerful (W/Test)

The Alen FLEX is one of the quietest air purifiers ever. Not only that, but it's also a great performer in neutralizing dust, smoke, pollen, and bad odors.

Our Verdict





Operating cost


Value for money


Ease of use




The Alen BreatheSmart FLEX is an excellent air purifier that has met all my expectations. It is a minimalistic device without many advanced features, but it boasts extraordinary filtration technology, amazing performance, and fantastic scores on all tests.

Aesthetically, it fits perfectly into almost any ambiance while also easily cleaning the room’s air.

If you’re looking for an air purifier for rooms up to 300 sq. ft. (28 m²) or even larger spaces, the Alen FLEX is a perfect choice, and I’m sure it won’t let you down.

The Alen FLEX is a definite choice and my absolute recommendation for purchase.

What we really like?

  • The Alen FLEX covers medium-sized rooms of 300 sq. ft. (28 m²), with an ACH of 4.8.

  • It uses premium-grade filtration consisting of a pre-filter, a True HEPA filter, and a pellet-based carbon filter.

  • This air purifier is a perfect choice for bedrooms, living rooms, kids’ rooms, kitchens, basements, and offices.

  • The Alen FLEX is one of the quietest air purifiers we tested, producing only 53.7 dBA at max speed.

  • In the 560 sq. ft. (52 m²) room test, it improved the air quality by an incredible 94%.

  • It’s energy-efficient, Energy Star certified, CARB-certified, and 100% ozone-free.

What could be better?

  • It comes with a lifetime warranty, but only if you regularly purchase replacement filters through the Alen website.

  • It lacks smart features such as an air quality sensor, smart app, and auto mode.


ModelBreatheSmart FLEX
Dimensions (inches / cm)8.5 x 15 x 25 inches (21,6 x 38,1 x 63,5 cm)
Weight (pounds / kg)15 lb (6.8 kg)
Clean Air Delivery Rate (CADR)245 CFM
Filtration TechnologyPre-filter, True HEPA Filter, and Activated Carbon Filter
Filter Replacement IndicatorYes
Filter Life9-12 months
Number of Fan Speeds4 – Speed 1, Speed 2, Speed 3, and Turbo Mode
Air Quality Sensor No
Air Quality IndicatorNo
Auto Mode No
Smart App No
Voice Control No
Other FeaturesControl Panel LockTimer
Coverage (4.8 ACH) 300 sq. ft. (28 m²)
Performance Ratings
Power Consumption 50W
Operating Costs Ratings
Noise Level (low – high)41.2 – 53.7 dBA
Noise Ratings
Best Suited For
Living Rooms
Neutralizing VOCs
Quiet Operation
Warranty1-year to Lifetime

Full Review

Alen is one of the leading manufacturers of air purifiers located in Austin, America. Their machines are characterized by pure elegance, good build quality, and excellent performance.

The Alen BreatheSmart FLEX is the smallest model in the BreatheSmart series. It is a modern, minimal, high-end air purifier designed for rooms up to 300 sq. ft. (28 m²). In fact, the Alen FLEX is a replacement for the Alen BreatheSmart 45i.

Alen BreatheSmart Flex Air Purifier - Review
I placed the Alen FLEX in my living room. Photo: / Milan Antonic

I have been following Alen in the air purifier market for some time now, and always wanted to test some of their products, esspecially the Alen FLEX. Although slightly more expensive than other air purifiers in the same class, the Alen FLEX has many things to show.

In this article, I will cover all the features and even the most minor details of this air purifier. I will test the performance, noise level, energy consumption, and all the options that the Alen FLEX offers.

In addition, I will touch on a few shortcomings, such as the lack of smart sensors and the auto mode option. This is going to be a very exciting review!

How We Tested the Alen FLEX?

1. For the filter efficiency testing, we used the Temtop LKC-1000S laser particle meter, which measures PM2.5 (µg/m3), PM10 (µg/m3), Particles (per/L), and HCHO (mg/m3) in the air, and also calculates the AQI.

2. We placed the Alen FLEX in two separate performance tests, one in a 560 sq. ft. (52 m²) room and the other in 730 sq. ft. (68 m²) room. Then, we recorded the initial air quality values using the Temtop laser particle meter and let the Alen FLEX run at maximum speed.

Alen BreatheSmart Flex Air Purifier - Performances Test
I used a Temtop laser particle meter to test Alen FLEX performance. Photo: / Milan Antonic

3. After 60 minutes, we measured the new values using the Temtop laser particle meter and saved the data.

4. Next, we placed the Alen FLEX in a glass box, which we then filled with smoke. Then, we measured how much time was needed for the air purifier to remove all the smoke from the box.

5. Using a special noise measurement tool, we tested the air purifier’s noise level at all speeds. We measured the noise level on the dBA scale.

Alen BreatheSmart Flex Air Purifier - Noise Test
I used a special tool to test Alen FLEX noise levels. Photo: / Milan Antonic

6. Finally, we measured the power usage at all speeds using an energy meter, after which we calculated how much it would cost to use the device at a particular fan speed for one month. For reference, we used an energy price of $0.12 per kWh.


Performance – Particle Removal Tests

The Alen BreatheSmart FLEX is an air purifier designed for rooms up to 300 sq. ft. (28 m²). Alen offers several different filters to choose from when purchasing the unit. The Alen FLEX that we tested uses the Dust, Mold, Pet Odor, and Smoke Filter.

In addition to the tests listed below, I also tested the Alen BreatheSmart FLEX in my place, where I spend most of the day. I have noticed a positive change in the air quality.

I have also used it several times in the kitchen to test how effectively it removes cooking odors, and it has shown excellent capabilities.

Additionally, the Alen BreatheSmart FLEX is, in my opinion, the best choice when buying air purifiers for the basement (which is why I put it on the list).

My advice is that if you are using the FLEX in a very crowded room, first turn it on in turbo mode for at least two hours and then set it to a lower speed. You can safely leave the Alen FLEX running 24 hours a day.

Testing in a 560 sq. ft. (52 m²) Room

The first test was conducted in a 560 sq. ft. (52 m²) room, which is larger than the recommended dimensions. I placed the Alen BreatheSmart FLEX in this room and let it run at full speed.

# Starting Baseline After 60min
PM 2.5 96.3 µg/m³ 5.7 µg/m³
PM 10 134.8 µg/m³ 8.1 µg/m³
Particles 139680 per/L 8399 per/L
AQI 126 8

In 60 minutes of operation, the FLEX improved air quality by an impressive 94%, lowering the PM2.5 particulate level from 96.3 to 5.7 µg/m³. This is an excellent result, especially considering the room is larger than the recommended dimensions.

Particle Removal Test Room - Comparison

Comparison between the Alen FLEX and its competitors in particle removal tests in a 560 sq. ft. (52 m²) room.

As you can see on the chart above, the Alen FLEX performed much better than some of the larger air purifiers. The DREO improved air quality by 88%, which is significantly lower; the Levoit Vital 200S also did 2% worse than the Alen, improving air quality by about 92%.

Testing in a 730 sq. ft. (68 m²) Room

In the second room, which is 730 sq. ft. (68 m²) and much larger than the recommended dimensions, the Alen FLEX improved the air quality by approximately 89% in 60 minutes of operation at maximum speed.

We placed it in this large room just to see how it could handle this ambitious challenge, and it did pretty well.

# Starting Baseline After 60min
PM 2.5 103.3 µg/m³ 10.8 µg/m³
PM 10 144.7 µg/m³ 15.1 µg/m³
Particles 149909 per/L 15671 per/L
AQI 135 15

Considering the size of the room and the challenge Alen faced, this is a more than good result. Honestly, I expected brilliant results from an air purifier like the Alen FLEX. I think it’s evident that the FLEX lived up to its name and delivered excellent results in both tests.

Performance – Smoke Removal Test

The Alen FLEX is a fantastic air purifier that performs excellently on all tests. However, it was somewhat slower on the smoke test compared to some devices in the same class. It took 32 seconds to remove all the smoke from the glass box, which was a bit slower than expected.

Alen BreatheSmart FLEX - Smoke Test
Alen BreatheSmart FLEX unique smoke test. Photo (GIF): / Milan Antonic

As you can see on the chart, I listed a small air purifier, the Philips Series 800, alongside similar competitors. Despite being much smaller and inferior to the Alen, it cleared all the smoke from the glass box in just 33 seconds, only one second slower.

Smoke Box Test - Comparison

In this chart, you can see how quickly the Alen FLEX removes smoke from a glass box compared to its competitors.

Don’t be confused by this. The reason is simple: the Alen FLEX uses a high-quality True HEPA and pellet-based activated carbon filter that are so densely made they slightly slow down the airflow, which is why it took the Alen a few more seconds to clear all the smoke from the box.

In essence, the Philips I mentioned doesn’t have a better filter; the Alen’s filter is denser, which slows down the airflow.

There are, of course, some superior air purifiers like the Blueair 211+, which took 11 seconds, or the Levoit Core 600S, which took 9 seconds.


Noise Levels Test

The Alen BreatheSmart FLEX is an amazingly quiet device. I have to say that I have never come across an air purifier like this. It’s so quiet at work, yet at the same time very efficient.

Alen is SleepScore certified, making it one of the quietest air purifiers ever and definitely one of the best options to use in bedrooms.

The Alen produces what is called Pink Noise, which helps you sleep easier, meaning you can use it in the bedroom without any problems. Some users can use it in the bedroom even at higher speeds.

Noise Levels Test - Comparison

This chart compares the noise levels at the minimum and maximum speeds of the Alen FLEX air purifier with those of its competitors.

See the chart above for a comparison of the Alen FLEX noise level with the noise levels of some similar or even larger air purifiers.

The Alen FLEX has four speeds, so you’ll find it easy to choose the one that suits you best. At the first speed, the FLEX produces a sound of only 41.2 dBA, but even more surprising is the turbo mode, where the FLEX makes a sound of only 53.7 dBA.

Fan Speed Alen FLEX (dBA)
Speed 1 (Low)41.2 dBA
Speed 2 (Medium)43.5 dBA
Speed 3 (High)48.9 dBA
Speed 4 (Turbo)53.7 dBA

I can say with certainty that this is one of the quietest devices I have tested to date. Despite being quiet, the motor produces a satisfying and pleasant sound, so using it in the room you are staying in won’t be a problem.


Operating Costs – Power Usage Test & Filter Price

In fact, the Alen BreatheSmart FLEX is an air purifier with a power consumption of only 50W. If you leave it at maximum speed, 24 hours a day, it costs about $2.13 per month, considering the average electricity price in the US is $0.12 per kWh.

Alen BreatheSmart Flex Air Purifier - Engine
The Alen FLEX uses a huge motor, as you can see in the image above. Photo: / Milan Antonic

This is one of the lowest power usage costs among all competitors. For example, the Levoit LV-H134 will cost you about $4.43, the DREO Macro MAX S will cost you $3.16, and the Levoit Vital 200S will cost you $4.23, which are all significantly higher than the cost of the Alen FLEX at maximum speed.

Monthly Power Cost – Comparison

Comparison of the monthly power cost at maximum speed between the Alen FLEX and some of its competitors.

Considering the dimensions of this powerful air purifier, you will agree that this isn’t a very high monthly cost. However, in addition to the cost of electricity, there are also the costs of replacing the filters, which are slightly more expensive.

Fan Speed Alen FLEX (W + $/month)
Standby0.4W ($0.04)
Speed 1 (Low)2.7W ($0.24)
Speed 2 (Medium)6W ($0.53)
Speed 3 (High)14.2W ($1.24)
Speed 4 (Turbo)24.3W ($2.13)

But, if you follow the guidelines I have advised in the filter section and clean the pre-filter regularly, the primary filter will likely last 12 months.

Putting everything together, we can say that the Alen FLEX air purifier’s annual maintenance cost isn’t too high.

Filtration Technology

Alen BreatheSmart FLEX offers several different filtering options; more specifically, it provides the choice of three different filters. Each of these filters differs most in the activated carbon filter. Each includes a True HEPA filter as a basic part of the package.

Alen BreatheSmart Flex Air Purifier - Filters
The image above shows the pre-filter and the True HEPA and Activated Carbon filter combination. Photo: / Milan Antonic

The optional filters are:

  • Dust, Mold, Pet Odors
  • Dust, Mold, Pet Odors + Smoke
  • Dust, Mold, Pet Odors + Heavy Smoke

The device I tested was equipped with the “Dust, mold, pet odors + smoke” filter, which proved to be a perfect choice considering the performance and efficiency that the device made with this filter.

Alen BreatheSmart FLEX - Replacement Filter

Alen BreatheSmart FLEX Replacement Filter

Always buy genuine filters for the best performance. As soon as the filter reset indicator is on, you are ready to change filters. Do it as quickly as possible.

Check Filter Price On Amazon

The filter is rectangular in shape and is located under a cover on the front of the air purifier. The Alen BreatheSmart FLEX tackles dust, allergens, pollen, fur, pet dander, household odors, cigarette smoke, fires, and VOC fumes from chemicals and aerosol sprays.

Alen FLEX has a filter cover check guard, so if you don’t close the cover properly, you won’t be able to turn it on.


The pre-filter is the first stage of filtration. It is attached to the True HEPA filter with a Velcro strap and can be detached if necessary. The pre-filter is designed to protect the True HEPA filter by preventing larger particles such as hair, fur, dander, and other larger particles from penetrating the HEPA filter, thus extending its life.

Alen BreatheSmart Flex Air Purifier - Pre-filter
A pre-filter. Photo: / Milan Antonic

As the pre-filter gets dirty very quickly, I recommend cleaning the pre-filter at least once a month with a vacuum cleaner to remove excess dust.

The True HEPA Filter

True HEPA is the second and main level of filtration and is most responsible for effectively filtering the air. BreathSmart FLEX contains a medical-grade H13 True HEPA layer that removes 99.99% of bacteria, aerosolized viruses, and airborne particles larger than 0.1 microns. True HEPA filters last 3-5 months longer than standard filters.

Alen BreatheSmart Flex Air Purifier - True HEPA Filter
A True HEPA filter. Photo: / Milan Antonic

Thanks to the combination of powerful airflow and a high-quality True HEPA filter, Alen FLEX is highly effective, and you will notice changes in air quality almost immediately.

Activated Carbon Filter

The activated carbon filter is the last, third stage of filtration. This is the filtering stage that is responsible for neutralizing gases, VOCs, and various other odors.

My absolute recommendation is to go for the carbon filter option, as this will ensure that you get the full potential from the Alen FLEX, and almost no situation will be able to take you by surprise.

Alen BreatheSmart Flex Air Purifier - Activated Carbon Filter
An Activated Carbon filter. Photo: / Milan Antonic

In this review, I tested an air purifier with a filter for dust, mold, pet odor, + smoke, as I mentioned earlier. This filter is unique because it has a carbon filter that contains 0.66 lbs of activated carbon. And that’s enough for some everyday situations, cooking and neutralizing everyday odors.

But suppose you still want even more efficient and powerful performance in the fight against gases. In that case, I recommend you choose the filter option for dust, mold, pet odors, + strong smoke because, in this case, the carbon filter contains 2+ lbs of activated carbon.

How to Replace the Alen FLEX Filter?

The Alen BreatheSmart FLEX uses a filter reset indicator that shows that it is time to change the filter when illuminated red. Filters on this model last on average 9-12 months. However, suppose you maintain your air purifier frequently and clean the pre-filter regularly. In that case, the filter will likely last a maximum of 12 months.

The filter replacement process is straightforward and not very different from the standard procedure we are used to with similar devices.

Total time: 10 minutes.

Step 1 – Remove a Cover

To begin, you need to switch off the Alen Flex and open the cover on the front.

Removing the filter cover from Alen FLEX.

Step 2 – Remove the Old Filter

The next step is to remove the old filter from the device.

Removing old filter from the air purifier.

Step 3 – Vacuum Inside the Device

After that, it would be good to vacuum up any dust residues on the inside of the front cover and in the areas where you notice the dust.

Vacuuming the air purifier.

Step 4 – Insert a New Filter

The fourth step is to unpack the new filter, prepare it for use and insert it into the device. Then close the filter cover.

Removing plastic bag from a new filter.

Step 5 – Reset the Indicator

The last step is to reset the filter reset indicator by holding your finger on the “Filter” button for 5 seconds.

Resseting the filter reset indicator.

Installation and Setup

As I indicated at the beginning of the review, the Alen FLEX is full of style. Although this is not directly related to the performance and efficiency of the device, I am always pleased when a manufacturer makes an effort to package an air purifier correctly.

After unpacking the Alen FLEX, peel off all the straps holding the front cover so that it does not come off during transport. Then, remove all other tapes and protective films from the control panel and other parts of the device.

The last and most crucial step is to prepare the filter for operation. You need to open the cover on the front of the device and remove the filters. Then remove the filters from the plastic packaging and return them to the device.

Once you have successfully completed all the steps I have mentioned, plug the Alen FLEX into the power supply and switch it on.

Alen FLEX is designed to run 24 hours a day without problems, primarily to achieve maximum efficiency.


The Alen BreatheSmart FLEX is a mid-size air purifier with a luxurious appearance and superior build quality. As soon as I touched it, I noticed the difference in the quality of the materials and the way the Alen FLEX is made. The plastic is much more robust, and the unit is tighter than some competing air purifiers in this class.

The slightly larger dimensions of the device are mainly due to the larger space, which houses a more powerful motor and the larger filter.

Alen BreatheSmart Flex Air Purifier - In-depth Review
The Alen FLEX is a stylish air purifier that will fit into almost any ambiance. Photo: / Milan Antonic

The length of the power cord cable, which is approximately 78 centimeters long, is commendable. The Alen FLEX is not only well made but also aesthetically “irresistible.” The designers have really worked on all the details, so you can choose one of 6 colors for the front plastic. The colors you can choose from are: brushed stainless, espresso, graphite, oak, weathered grey, and white. As you can see from the pictures, I have chosen the most neutral color for this test, white.

I would like to point out that what I consider necessary, especially with such slightly larger air purifiers, is the slot for easier carrying of the appliance, located at the back of the Alen, on top of the device.

Alen BreatheSmart Flex Air Purifier - Backside
There is a carrying handle on the back side of the air purifier. Photo: / Milan Antonic

I would like to point out that you can buy each color separately later and switch them as you want

Alen FLEX easily fits into almost any ambiance thanks to its design options, whether you plan to keep it in a luxurious or less luxurious room.

When you place the unit in the desired location, move it at least 20 inches away from the wall and other objects.

Control Panel

At the top is the control panel, which contains 5 touch keys. Alen’s logo is elegantly embedded on the board next to the buttons. The power button is the central button; it is the largest and most important compared to the other buttons. Pressing the power button starts the Alen.

However, this button has another hidden function, so the next press dim all the LED indicators, which is helpful for people who intend to use the device in the bedroom. When the device is switched on, the blue indicator around the power button lights up.

Alen BreatheSmart Flex - Control Buttons
The touch panel with buttons and indicators is located on the top of the device. Photo: / Milan Antonic

On the far left is the filter button, above which are indicators to show the current wear of the filter. Just to the right of this is the timer button, above which there are also indicators.

Moving on, there is a speed button to switch between one of the four speeds.

Last is the lock button, which locks all the other buttons against accidental pressing or switching off the device.


The airflow of the Alen FLEX reminds me very much of the Winix 5500-2 and the Coway Mighty air purifiers. Moreover, I can say that it is almost identical.

The Alen draws air from the front, the vents on the sides, and the bottom. The air is then filtered and exits towards the ceiling through vents at the back of the unit.

Size and Dimensions

The air purifier weighs 15 lb. The dimensions of the unit are 8.5 x 15 x 25 inches.

What’s in the box?

You get a BreatheSmart FLEX air purifier, HEPA Pure filter, a design plate (optional), and a quick start guide in the package.

Alen BreatheSpace FLEX is specially packaged and requires additional preparation before the first start-up, so I recommend you read the procedure to get the device ready for operation if you haven’t already.

Features Overview

The Alen FLEX is a minimal air purifier without many complicated controls and advanced options. To be honest, it may be a drawback that a device in this price range lacks a smart sensor and an auto mode. Still, fortunately, Alen has compensated for these shortcomings with outstanding quality and excellent performance.

Alen BreatheSmart Flex Air Purifier - In front of the desk
I placed the Alen FLEX in front of my office desk. Photo: / Milan Antonic

This is still a smaller, cheaper, and minimal model, but if you want a model with more advanced options, you can look at the FIT50, the Classic, or some other model from Alen.

Switching off the indicator on the device

Alen FLEX does not have a dedicated button to switch off the indicator lights on the devices. However, when the device is switched on, pressing the power button turns off all the indicators. The next time the same button is pressed, the air purifier will switch off.


A timer is a great option that is very useful. Especially since Alen has no other option for “programming” the operating mode than the timer option.

The timer, when active, turns the Alen FLEX off after time is up, which can be 2 hours, 4 hours, or 12 hours.

Filter Reset Indicator

I love this option, and so far, I have rarely come across an air purifier that does not have a filter reset indicator (and there have been examples, one of them being the HathaSpace HSP001).

Thanks to the filter reset indicator, you won’t have to think about when it’s time to change the filter on your air purifier. The FLEX will let you know when you need to change the filter.

Above the “Filter” button, there are three round indicators; only one indicator will be green when you start using the device. When the yellow indicator appears, it means it’s time to change the filter soon, and only when the red one appears, you need to change the filter on the device.

Control Panel Lock

This is the ideal option for locking all commands on your device. This feature is handy if young children might accidentally turn off the device or change the mode.

The lock button is activated by holding your finger on the lock button for 5 seconds. After that, pressing any other button will not register.

Room Coverage and CADR

Alen BreatheSmart FLEX has a CADR score of 245. This means it can capture a small air pollutant better than the average air purifier and with greater efficiency.

The Alen FLEX is designed for rooms up to 300 sq. ft. In a room of this size, the FLEX will clean the air twice an hour. Ideal for any room, from small to huge bedrooms, living rooms, offices, nurseries, kitchens, and basements.

Alen Customer Support and Warranty

In talking to some users, I have concluded that the customer support of the Alen BreatheSmart FLEX is of a high standard.

When you buy the product, a leaflet in the box contains the contact details for support. Alen suggests calling the phone number or contacting via the website.

Alen BreatheSmart Flex Air Purifier - Test
The Alen FLEX offers a highly generous lifetime warranty. Photo: / Milan Antonic

I have tried the support via the website. I have chatted with the support and asked them basic questions, which I have received satisfactory answers to in a relatively short time.

It is important to note that chat support does not always work, so if you do not wish to contact them via phone number, you can send them an email. You can also expect a relatively quick reply.

Apart from the support, the warranty is another thing that triggers many users who decide to buy the Alen BreatheSmart FLEX air purifier.

The reason for this is that Alen offers a lifetime warranty on all air purifiers. Of course, there is one catch. To access the lifetime warranty, you must subscribe to buy replacement filters for your Alen FLEX air purifier on an annual basis via the website.

FAQ on Alen FLEX

Does the Alen BreatheSmart FLEX produce ozone?

The Alen FLEX does not use an ionizer or other filtration system that could produce ozone. Therefore, this device is 100% ozone-free and safe to use.

How often do I need to change the filters?

The filters on the Alen BreatheSmart FLEX air purifier last on average 9-12 months. This means that the filters should be replaced on average once a year when used optimally.

What is the warranty on the Alen FLEX?

Alen provides a lifetime warranty on this model if you register the product on the website and have an active subscription for replacement filters.

2 responses to “Alen FLEX Air Purifier Review: Quiet and Powerful (W/Test)”

  1. Gabriel Alvarez

    I am very impressed with your reviews. I am also overwhelmed with the many choices. Can send me some recommendations-to narrow down my choices- and according to my specific health situation of COPD?

    • Milan Antonic

      Thanks for your kind words! I recommend speaking with your doctor since they are better equipped to provide suggestions and insights based on your health situation.

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