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Alen BreatheSmart Flex VS 45i

They look identical but are they exactly the same? Our side by side comparison will help you figure that out
By
Updated on March 18, 2024
Written by
Teddy Booth
Teddy joined HouseFresh in 2019 as a senior content producer, producing written content as well as product photography and YouTube videos. He supports Danny as a product tester and is our lead how-to writer.

Our verdict

When it comes to design and filters, both units are almost identical. The differences come from the added features and costs. 

 

We’ve chosen the Flex as our overall winner as its initial price, annual running costs and cleaning performance proves that it works harder than the 45i.

Alen are known worldwide for their range of air purifiers. This Austin-based company has been engineering and innovating since 1999, so they have a wealth of knowledge behind them. Their mission is to ” improve the quality of people’s lives” with their products; their vision is to “inspire a healthier life and provide peace of mind” for their customers.

Known for their simple yet elegant designs and heavy-duty filters, Alen air purifiers are extremely popular and trusted throughout the world. That’s why we wanted to get our hands on a few of their products to test and review.

First, we bought the BretheSmart 75i, which showed us how powerful Alen units can be. We then chose the BreatheSmart 45i, which was, again, very impressive. So we had to check the BreatheSmart Flex to see if Alen could keep up this streak (spoiler alert…it did).

As the 45i and Flex were so similar in size, we wanted to pit them against each other. This guide compares their test results, specifications, design, controls, filters, performance, sound and running costs to see which unit best suits your needs and budget.

  1. In our home lab of 728 cubic feet, we light an incense stick to generate particle pollution and VOCs.
  2. We set up our trusted Purpleair Indoor Sensor with the latest Bosch gas sensor to track levels of PM1ug/m3, PM2.5ug/m3 and PM10ug/m3 and VOCs in the air.
    purpleair
  3. We switch the air purifier to its highest speed and measure how long it takes to get our room air quality down to PM1 level to 0.
  4. We use an energy meter to measure precisely how much electricity is used when running the unit at the lowest and highest fan speed settings.
  5. We track sound levels emitted by the air purifier at different fan speeds with the help of a commercial sound meter.
    sound meter

TL;DR Which unit wins overall? 

“The Alen Flex is best for most people and is a one of our favorite air purifiers for a medium sized space and allows for choice of filters and has Alen’s lifetime warranty for the lowest possible price. Yet I still run a Alen 45i in my office as I appreciate the auto-mode but it comes at a price bump that you should be aware of.”
— Danny Ashton, HouseFresh Founder & Senior Writer

Don’t want to read the full article? Don’t worry; I’ll condense it.

The pros and cons compared

BreatheSmart 45iBreatheSmart Flex


What we really like

👍 App connectivity
👍 Ionizer is optional
👍 Very quiet at low fan speeds
👍 Has an auto mode
What we really like

👍 Lower price than the 45i with similar CADR
👍 Energy efficient
👍 Four filters to choose from
👍 Lifetime warranty
What we think could be better

👎 Looks plain
👎 Not as energy efficient as the flex
👎 Cheapest filter option doesn’t have activated carbon
What we think could be better

👎 No auto mode or app support
👎 Higher filter costs than some other brands
👎 Control panel is a little basic

The specifications compared side-by-side

When it comes to specs, the 45i is the winner as it’s lighter, quieter and, due to its higher CADR, tackles pollutants in larger rooms than the Flex.

When we compare two units side-by-side, we first look at their cleaning power. This is called CADR (Clean Air Delivery Rate) and is measured in CFM (Cubic Feet per Minute) to show us how effective an air purifier is at its job.

The 45i boasts a higher CADR at 245 CFM whilst the Flex falls slightly behind at 225 CFM. But, when we put these two units through our performance tests, that extra 20 CFM only translated to one-minute difference to clean the contaminants from our room. 

It may win on paper, but the price difference between the 45i and the Flex is around $70 for that extra minute of cleaning performance.

Tip

Want to know more? Check out our full guide on What Is CADR Rating?

BreatheSmart 45iBreatheSmart Flex
HouseFresh Rating:★★★★☆★★★★☆
Time to clean our test room:33 minutes34 minutes
Air purifier technology:True HEPA H13 filters with activated carbon pellets + Ionizer technologyH13 HEPA with an option for activated charcoal pellets
Recommended room size:Up to 800 sq. ft. Up to 700 sq ft
Clean air delivery rate (CADR):245 CFM225 CFM 
Dimensions (in inches / in cm):25H x 15W x 8.5D inches inches (63.58H x 38.1W x 21.5D cm)25H x 15W x 8.5D inches (63.5 x 38.1 x 21.59 cm)
Weight (in pounds / in kg):9.1 kg (20.1 lbs)15 lbs (6.8 kg)
Filter life:12 months12 months
Noise level (low – high):23dB – 49dB25 – 50dB
Estimated energy consumption:$52.56 per year$25.23 per year 

The design elements compared

When it comes to the design aesthetics, it’s a draw as these two both look virtually identical.

The technology inside these two units may differ, but looking at them side-by-side, you’ll see they are practically exactly the same. It’s too close to call a winner.

The subtle differences lay in the grill at the top of the unit, where the 45i has bigger square holes than the Flex and the control panel (which we’ll go into later) and the 45i sits a little higher on its stand. 

The 45i is lighter, so it is easier to move, but they both feature a flat, removable front panel held on with magnets, curved edges and measure up the same size. To the untrained eye, you would never be able to tell the difference.

Ease of use and control panel compared

Regarding the control panel, the winner has to be the 45i thanks to its extra features, including an auto mode, ionizer and display brightness control.

They may be identical from the front, but when you look from above, you’ll see the differences on the control panel. Let’s start with our winner, the 45i.

Seven touch-sensitive round buttons are placed along the black glossy top of the 45i to adjust its settings.

  • Ionizer releases electrically charged particles into the air that cling to pollutants and force them to the ground
  • Filter indicator with three lights (green, yellow, red) to warn you when the filter needs to be replaced
  • Light adjusts the brightness of the display between low, high and off
  • Power button in the center to turn the unit on and off
  • Speed switches between its four fan speeds (with the highest being Turbo speed)
  • Auto engages auto mode, where the unit uses data from its air quality sensor to adjust the fan speed according to the amount of pollutants in the air.
  • Lock allows you to disable the control panel after pressing and holding it for three seconds 

Sometimes, you’ll find that air purifiers with touch-sensitive controls are lacking on the “sensitive” part, making them hard to operate. This isn’t the case with Alen air purifiers. From the units we’ve reviewed, we found the controls very easy to press, and little force is needed to activate them.

The display is bright enough to be seen in daytime but not so bright that it’s distracting, and the addition of a brightness control and the option to turn them off completely makes it even better.

We’re still not sold on ionizer technology, but the fact you can leave it turned off is better than it running constantly.

Both units come with an AQI (Air Quality Indicator) color wheel in the center of the control panel. Using data provided by the air purifier sensors, this light displays the air quality in your room using five colors. 

ColorAir Quality
PurpleVery poor
RedPoor
OrangeAverage
GreenGood
BlueVery good

The biggest difference between the features on the 45i and Flex is that the 45i comes with an auto mode. This uses the same air quality information from its sensor to adjunct the fan to suit the amount of pollutants in the air.

The Flex only has five buttons on its control panel: Filter, Timer, Power, Speed and Lock. The lack of auto mode is a detractor for me (you may not need one), but the addition of a timer is nice.

For all you tech heads out there, Alen has developed their own BreatheSmart smartphone app that connects to your unit through Wi-Fi or Bluetooth. Once connected, the app allows you to monitor the air quality in your room and control the unit settings from anywhere in the world.

The app is easy to navigate and control, and it looks great. Plus, you can add/monitor/control more than one BreatheSmart air purifier if you have them in multiple rooms. The app is available for iPhone and Android devices.

Air filtration technology compared

In terms of filtration technology, we face another draw: both units use the same filter technology.

Through our performance testing, we were impressed with all the filters from the Alen products we reviewed. Alen shows they mean business by only including heavy-duty, thick H13 (medical grade) HEPA filters with activated carbon pellets in their units.

As the 45i and Flex are the same size, Alen decided they could use the same filters for both. So that’s exactly what they did.

What differentiates these two air purifiers from many other models is that you can choose from five different variations of H13 HEPA filters to customize your unit to your needs and wants.

B4-Pure FilterCaptures allergens, dust, mold, and germs
B4-Fresh FilterAll of the above + carbon to absorb common household odors 
B4-Odor FilterAll of the above + odor neutralizer to absorb pet odors and other unwanted smells 
FL40-H Heavy Smoke FilterAll of the above + 2.3 lbs of active carbon to absorb chemicals, VOCs and smoke

Each filter available uses H13 HEPA technology that is capable of trapping 99.9% of airborne particles as small as 0.1 microns (dust, dander, allergens, mold, bacteria and viruses).

With the exception of their basic B4-Pure filter, they contain various levels of activated carbon pellets. This is used in filters because of its ability to adsorb odors and other VOCs (Volatile Organic compounds). The more activated carbon a filter contains, the more contaminants it can remove.

If your home isn’t affected by many pollutants, we recommend you go for the B4-Fresh Filter. Suppose you’re buying an air purifier because your home is heavily polluted (e.g. wildfire smoke), we suggest you opt for the stronger FL40-H Heavy Smoke Filter that contains 2.3 lbs of activated carbon.

Segue sentence to introduce the concept of filter replacement. Here is what you can expect from both units when it comes to replacing the filters:

Tip

When you first unbox your Alen air purifier, be sure to remove the plastic packaging from the filter before you start using the unit. If you don’t, the filter won’t do its job, and the plastic may start to burn over time.

Air cleaning test results compared

When it comes to air cleaning performance, the Flex wins. The 45i may have been faster by one minute, but the Flex has a lower CADR, so it worked much harder to get its result. 

If you’ve read a review on HouseFresh before, you’ll know that we test every air quality product we recommend in our own home lab. The Alen BreatheSmart Flex smashed the tests.

At HouseFresh, we don’t rely on manufacturer data for three main reasons:

  • Some air purifiers are tested in laboratory conditions; some are not
  • Manufacturers use different methods and equipment from each other
  • Some manufacturers may lie about their results

We knew that if we wanted to compare units side-by-side, we had to conduct our own performance tests under the same conditions and because you’re gonna be using your air purifier in your home, we want to test them in ours.

Every unit we review goes through the same performance tests where we fill our office (705 cubic ft) with simulated pollutants. We then turn the air purifier on at full fan speed to see how long it takes them to remove all the contaminants from the room.

Using our indoor sensor from Purpleair, which provides continual updates on PM1.0ug/m3, PM2.5ug/m3 and PM10.0 ug/m3, we monitor and collect data from every step of the process.

For an air purifier of this size and cost, we expected to see these two units give us a time of around 30 minutes, but we didn’t predict the difference to be so minimal.

Both units performed well in our performance testing room, with the 45i clearing all of our simulated contaminants from the air in 33 minutes and the Flex in 34 minutes

Even though the 45i had a better time, it was by only 1 minute. This shows that the Flex is working harder overall as it has a lower CADR of 225 CFM compared to the 45i, which has 245 CFM.

With their performance times so close, this shows that you’re paying those extra dollars on features, not performance. So take that into serious consideration when choosing which unit suits your needs.

Tip

If your main focus is performance, check out the Levoit EverestAir that cleared our performance room in 13 minutes.

The 45i cleared our test room in 33 minutes

The Flex cleared our test room in 34 minutes

When we look at the data side by side from the Flex and 45i, it becomes clear how close they are in cleaning performance. With only a minute between them, the Flex works harder than the 45i to match its results. You probably won’t be able to tell the difference in a smaller room.

To see the performance of these two units on a larger scale, we compare the data next to that of other units of similar size/price/CADR that we’ve tested. As you can see, they sit quite far down the list, but not a million miles away from the competition. 

Noise levels test results compared

When it comes to the sound emitted, the winner is the 45i, as it generates less noise. Although the 45i is only one decibel quieter than the Flex when running at its highest fan speed level.

Even though some manufacturers use buzzwords like “Whisper quiet” and “near silent,” air purifiers move air through their filters using a fan that is powered by a motor. This means all air purifiers generate sound. But some make more noise than others.

Both units have four fan speeds, including T for Turbo, so you would expect that they would emit the same amount of noise. But the Flex is ever so slightly louder than the 45i on paper, though we doubt you’d notice the difference with them running side by side.

BreatheSmart 45iBreatheSmart Flex
Noise level (low – high):23dB – 49dB25 – 50dB

We’ve added this extra decibel to the Flex, working a little harder to match the 45i’s cleaning performance.

When you compare these two to some of the other air purifiers we’ve reviewed of similar size, you’ll see they are a little louder. But, 50dB (the loudest the Flex is at its highest fan speed) is equivalent to faint background music or a quiet office.

Tip

We don’t all know how loud decibels are and what some people consider loud, others may not. That’s why we take videos of all the air purifiers we review, recording each unit at their different fan speeds.

Check out both units here and see if you can tell the difference.

Cost to run each unit compared

Regarding long-term costs, the clear winner is the Flex. The filters may cost the same, but the Flex triumphs when it comes to energy efficiency.

1. Yearly electricity costs = $25.23 (Flex) versus $52.56 (45i)

As they are electrical devices, air purifiers need energy to run. It’s recommended that you run your air purifier 24/7, so the more energy-efficient a unit is, the less it will cost you in the long run.

Depending on what unit you buy and the state you live in, the cost of running your unit will vary, and with energy costs rising each year, it’s something you should look into before purchasing an air purifier.

The difference in energy costs between the Flex and 45i is very noticeable. The annual cost of running the 45i can come to double what it costs to run the Flex, meaning it’s a hell of a lot more energy efficient.

2. Yearly filter costs = $89 (Flex) versus $89 (45i)

Another consideration you need to make when buying an air purifier is the cost of replacing the filters. The filters in air purifiers need replacing periodically (the manufacturer will tell you how long they last on average), and it’s not recommended that you wash them.

Both of our units will indicate when it’s time to replace your filter when three lights illuminate over the Filter button. Remember, if you don’t replace your filter when instructed to do so, your air purifier won’t run at maximum efficiency.

As both units use the same filters, the annual costs are the same. We’ve calculated this using the B4-Fresh filter, which we recommend for most household pollutants.

The filter in the Flex and 45i should be replaced every 12 months: 

Alen Air Filter B4-Pure Replacement H13 True HEPA Filter for BreatheSmart 45i & Flex Air Purifier - Captures Allergens, Dust, & Mold (1 Filter)
Alen Air Filter B4-Fresh Replacement HEPA Filter for BreatheSmart 45i & Flex Air Purifier - Captures Allergens & Mold + Odors & Smoke (1 Filter)
Alen Air Filter B4-MP-Odor Replacment HEPA Filter for BreatheSmart 45i & Flex Air Purifier - Captures Allergens & Mold + Pet Dander & Odors (1 Filter)
Alen Air Filter FL40-H VOC/Smoke Replacement HEPA Filter for BreatheSmart 45i & Flex Air Purifier-Captures Allergens & Mold + VOCs & Smoke (1 Filter)
Technology
Medical-grade H13 HEPA Air Filter
Medical-grade H13 HEPA Air Filter with Odor Neutralizer
Medical-grade H13 HEPA Air Filter with Carbon
Medical-grade H13 HEPA Air Filter with Extra Carbon
Good for
Capturing allergens, dust, mold, and germs
Neutralizing pet, diaper, and other stubborn household odors + capturing pet dander, allergens, dust, mold, and germs
Absorbing harmful chemicals and VOCs, cooking odors, and common household odors + capturing allergens, dust, mold, and germs
Absorbing noxious gases from wildfire smoke and secondhand smoke, harmful chemicals and VOCs + capturing allergens, dust, mold, and germs
Price
$63.00
$89.00
$99.00
$119.00
Alen Air Filter B4-Pure Replacement H13 True HEPA Filter for BreatheSmart 45i & Flex Air Purifier - Captures Allergens, Dust, & Mold (1 Filter)
Technology
Medical-grade H13 HEPA Air Filter
Good for
Capturing allergens, dust, mold, and germs
More information
Price
$63.00
Alen Air Filter B4-Fresh Replacement HEPA Filter for BreatheSmart 45i & Flex Air Purifier - Captures Allergens & Mold + Odors & Smoke (1 Filter)
Technology
Medical-grade H13 HEPA Air Filter with Odor Neutralizer
Good for
Neutralizing pet, diaper, and other stubborn household odors + capturing pet dander, allergens, dust, mold, and germs
More information
Price
$89.00
Alen Air Filter B4-MP-Odor Replacment HEPA Filter for BreatheSmart 45i & Flex Air Purifier - Captures Allergens & Mold + Pet Dander & Odors (1 Filter)
Technology
Medical-grade H13 HEPA Air Filter with Carbon
Good for
Absorbing harmful chemicals and VOCs, cooking odors, and common household odors + capturing allergens, dust, mold, and germs
More information
Price
$99.00
Alen Air Filter FL40-H VOC/Smoke Replacement HEPA Filter for BreatheSmart 45i & Flex Air Purifier-Captures Allergens & Mold + VOCs & Smoke (1 Filter)
Technology
Medical-grade H13 HEPA Air Filter with Extra Carbon
Good for
Absorbing noxious gases from wildfire smoke and secondhand smoke, harmful chemicals and VOCs + capturing allergens, dust, mold, and germs
More information
Price
$119.00

HEPA filters trap airborne pollutants in their tightly woven maze of fibers (think of a fly in a spider’s web), removing them from the air. Space inside the filter gets smaller as more and more pollutants become trapped, making the filter less effective.

Replacing your filter periodically ensures you’ll have plenty of room to trap those harmful contaminants from the air in your home.

Want to know more? Check out our full guide How Long Do HEPA Filters Last?


Bottom line: Should you get a 45i or a Flex?

These two air purifiers may have many similarities, but their unique characteristics will sway you towards one or the other. 

If you want an energy-efficient air purifier that works hard with lower annual running costs — go for the BreatheSmart Flex. 

✅ If you want to pay a little extra for features like an auto mode and the choice of ionization — go for the BreatheSmart 45i.

It was a close call between the 45i and the Flex regarding design, filters and the numbers, with only one minute to separate them in our cleaning performance tests. The difference comes with the features included and the annual running costs. 

When you’re choosing which unit best suits your needs, you’ll need to think about what is more important: features or energy efficiency.

At HouseFresh, we have been reviewing air quality products since 2010. In all these years, we learned not to rely on manufacturers’ claims and the ever-so-glowing marketing materials. That is why we buy products with our own money, so we can write unbiased reviews after we’ve had enough time to evaluate air quality products in our home lab. Every unit we recommend has been thoroughly tested to assess its performance, energy consumption, and noise levels emitted in real-life environments. If you have any questions about our testing process for different types of air quality products, just drop us an email at hello@housefresh.com.

SOURCES

We calculated the monthly energy consumption costs with the help of the Department of Energy’s appliance energy calculator. We calculated yearly costs associated with running both units for 24hs a day for 365 days. We ran this calculation utilizing the U.S. average utility rate of $0.12/kWh as of October 6th, 2023. 

Last update on 2024-04-21 / Affiliate links / Images from Amazon Product Advertising API

About the author

Teddy Booth

Teddy joined HouseFresh in 2019 as a senior content producer, producing written content as well as product photography and YouTube videos. He supports Danny as a product tester and is our lead how-to writer.