Alen BreatheSmart 35i air purifier review — A real treat for gadget enthusiasts

Alen is a Texas-based company that makes smart-enabled air purifiers with customizable panels and air filters. Most of their appliances are designed for large spaces and come with relatively steep price tags (the flagship BreatheSmart 45i, for example, covers a whopping 950 square feet and costs a minimum of $449). However, the company has recently deviated from its strategy by offering a model that suits smaller spaces and tighter budgets — the Alen BreatheSmart 35i. This air purifier covers spaces of up to 500 square feet and costs a more affordable $269 (or $284 if you opt for customizable filters).

Specs-wise, it has the potential to land in our guide to the best air purifiers on the market. The Alen BreatheSmart 35i is quiet, compact and app-connected, plus it features a medical-grade H13 HEPA filter, a host of smart features and comprehensive air quality monitoring. We have been eyeing the Alen air purifiers for a while now, so when we were offered an opportunity to review the BreatheSmart 35i, we jumped on it without hesitation. Here's what we think of it after three months of testing.

Alen BreatheSmart 35i air purifier review

Alen BreatheSmart 35i: Design

• Plain, unobtrusive design
• Light, compact and portable
• Wide grille in the air vents

Visually, the Alen BreatheSmart 35i does not deviate significantly from other air purifiers — it is a white, rectangular block with a control panel at the top and air vents at the back of the unit. It does not have the artistic flair of the RabbitAir A3 or the multi-purpose design of the SwitchBot Air Purifier Table, but it is unobtrusive, easy on the eye and can easily fit in with most home decor. It is also relatively light and compact. The Alen BreatheSmart weighs only 11 lbs (5 kg) and measures just 20.6 inches (52 cm) in height and 7.6 inches (19.3 cm) in depth. We had no issues moving it around the house, and thanks to its large, built-in handle, we could easily grab hold of this air purifier with one hand.

Still, we were not too keen on its design. The Alen BreatheSmart 35i is made mostly of plastic, which makes it feel slightly flimsy and prone to scuffs. It does seem to lack the premium feel typical of some other appliances in this price range. More importantly, the air vents in this air purifier have an unusually wide grille. While this design tweak may improve the air flow, it can also create some other problems, especially for pet owners and parents of young children — a grille with large holes may easily fall prey to curious paws or small hands. There is also a risk of damage to the purifier's internal structures if some small items (food crumbs or toys, for example) end up falling through its cracks. That said, the Alen team assured us that, historically, this has not become a customer satisfaction or warranty issue, and all of Alen’s air purifiers meet the industry‐standard ETL safety and quality certification.

On the bright side, the Alen BreatheSmart 35i is easy to assemble and comes with a choice of customizable filters. We tested the basic version, called 'Pure', which features a H13 HEPA filter (a high-efficiency air filter designed to capture a minimum of 99.95% of airborne particles as small as 0.3 microns, such as grass pollen and mold spores), but you can also opt for the 'Fresh' option, which comes with an additional activated carbon filter (a type of filter designed to reduce gaseous pollutants like smoke and VOCs), or the 'Odor' version, which features the aforementioned H13 HEPA filter as well as a second filter that helps neutralize pet, diaper, and other common household smells. Filter customization is a big point for us — different pollutants require different technological solutions, and we can only applaud brands that recognize that no two households have the same issues with air quality.

Speaking of filters, they last approximately six to 12 months, and each costs around $54 to replace — on the expensive side, but well within the industry standard. Plus, they are slightly cheaper with an active subscription available through the Alen website.

Alen BreatheSmart 35i: Features

• Comprehensive real-time and historical air quality data
• Features auto mode, sleep mode and four manual fan speeds
• Ability to simultaneously connect up to 2,000 air purifiers in the app

This air purifier may not have the looks, but what matters more is what it can do — and it can do a lot. The Alen BreatheSmart 35i costs less than $280, but its smart features match or even outperform those found in much pricier units. For example, its robust air quality monitoring puts this air purifier on par with the Molekule Air Pro, an ultra-premium device that costs over $1,000. True, the Alen BreatheSmart 35i is not yet compatible with smart home apps like Alexa or Google Home, which does chip away slightly at its overall functionality, but we would still recommend it to any gadget fans out there.

The Alen BreatheSmart 35i can be operated both manually, through the control panel on the top of the unit, or remotely via the Alen app. This air purifier features four fan speeds, an Auto mode in which a built-in particle sensor detects air quality levels and adjusts the fan speed accordingly, and a Sleep mode that is essentially an Auto mode with quieter settings. It also has an LED indicator ring on the front that changes color (blue, orange, red or purple) to indicate current air quality, while more detailed air quality readings can be accessed in the app.

Speaking of the air quality sensors, the Alen BreatheSmart 35i measures PM 2.5 (airborne particles measuring less than 2.5 microns in diameter, such as smoke or dust mite allergens), TVOC (volatile organic compounds, such as chemicals found in paints and air fresheners), CO2 (carbon dioxide), temperature, and humidity levels, with both real-time and historical measurements available on the app. The Alen BreatheSmart 35i also analyzes the readings and provides you with personalized air quality tips, as well as notifies you if there is a sudden spike in specific pollutants.

The Alen app also allows you to keep track of remaining filter life, set schedules and monitor the outside air quality based on the provided location — all pretty standard features these days. What makes it truly stand out among other air purifier apps is its ability to simultaneously connect with up to 2,000 units. This means that the Alen BreatheSmart 35i can easily function within a huge network of interconnected air purifiers, and as such, it can be an excellent choice for schools, offices, commercial premises and any other spaces that may require multiple units with advanced air quality monitoring.

The cherry on top is that the Alen BreatheSmart 35i is certified Asthma & Allergy Friendly, meaning it has undergone rigorous, independent testing and is proven to be suitable for individuals with asthma, allergies, or other respiratory issues.

Alen BreatheSmart 35i: Performance

• Responsive and accurate air quality sensors
• Impressive air-cleaning performance
• Whisper-quiet and pleasant on the ears

The Alen BreatheSmart 35i performs exceptionally well, both in terms of sensing airborne pollutants and removing them from circulation. We spent around three months trying and testing this air purifier, and we were impressed by how quickly it detected and removed various air pollutants, from dust and pollen coming in through an open window to chemical smells from cleaning products and lingering perfumes. We also liked how quiet it was. Most of the time, we could barely hear it working.

When we measured its noise levels with a Sound Meter decibel-counting app, they ranged from 28 decibels (dB) on the lowest setting (equivalent to a whisper) to 45 dB on the highest fan speed (comparable to sounds you would hear in a library). Interestingly, the Alen BreatheSmart 35i sounded different from pretty much every other air purifier we tested. Typically, most devices produce a continuous mechanical white noise. This air purifier, however, sounds more like water being boiled in an electric kettle (if you are British, you know exactly what we mean!). We liked that — the Alen BreatheSmart 35i is surprisingly pleasant to the ear and, dare we say, quite relaxing to listen to. If you cherish a good night’s sleep, it will do a splendid job as a bedroom air purifier.

Now, let's move on to the specs. According to the brand, the Alen BreatheSmart 35i can purify air once every 30 minutes in spaces of up to 500 square feet — and this claim is in line with its CADR ratings. These independent metrics, measured in cubic feet per minute (CFM), indicate how quickly an air purifier can clean the air in a given space. For the Alen BreatheSmart 35i, CADR ratings are as follows: 180 CFM for smoke, 195 CFM for pollen, and 190 CFM for dust.

That said, we would recommend sizing down here. That is because two changes of air per hour may not be enough to achieve the best results, and most air quality experts advise at least four changes per hour. So, how does that apply to the Alen BreatheSmart 35i? To calculate the space the air purifier can clean in 15 minutes, look at its CADR ratings — they should be at least two-thirds of the room's square footage. Based on these stats, the Alen BreatheSmart 35i is likely to perform best in rooms measuring around 250 - 300 square feet (23.2 - 27.8 square meters). Luckily, this was exactly the square footage of one of our rooms, which is why we picked it to conduct our air quality tests.

We used our trusted Perfect Prime air particle monitor to measure air quality readings before and after running the Alen BreatheSmart 35i in several different circumstances. First, we did an ambient test. We placed the air purifier in a closed, aired-out room, then ran it on Auto mode for 30 minutes. After the first 15 minutes, we noted a 67% reduction in particles measuring 0.3 microns, and a 59% drop in air pollutants measuring 2.5 microns. After another 15 minutes, these values increased to 79% and 83%, respectively. These numbers may not sound particularly big, but we have to account for the fact that our baseline air quality was already relatively good on that day.

Next, we tested the Alen BreatheSmart 35i against heavier air pollution. We started by burning 10 matches and then running it on Auto mode for 30 minutes. After the first 15 minutes, 0.3-micron particles were reduced by 91%, 2.5-micron pollutants dropped by 95% and the largest 10-micron particles decreased by 99.8%. After another 15 minutes, these values increased to 99.8%, 99.9% and 100%, respectively. When we repeated this test at its highest fan speed, the Alen BreatheSmart 35i removed almost all pollutants within the first 15 minutes. We obtained equally impressive results in our incense tests when we burned five sticks and ran the air purifier to clean up the smoke.

During every test, we compared the results obtained with our air particle monitor with the air quality measurements taken by the air purifier. They were strikingly similar, with only a few small differences. If precision is your priority, the Alen BreatheSmart 35i will not disappoint you here.

Alen BreatheSmart 35i: User reviews

At the time of writing this review, the Alen BreatheSmart 35i scored 4.2 out of 5 stars on Amazon and 4.3 out of 5 stars on Best Buy. This air purifier was often praised for its user-friendly controls, compact design and great performance, with many users speaking highly of its quiet fans and ability to improve their allergy symptoms. Negative remarks, on the other hand, often revolved around its problematic app sign-up process, plastic build and relatively high price.

As one user commented, "[The Alen BreatheSmart 35i] is worth the price for me. It easily fits between my closet door and the cabinet, it is quiet and easy to operate with the touch buttons on the top. [However], I'm not a fan of the app. Start your account online or know an easy-to-remember eight-character password that includes a capital letter, a number and a special character. I tried setting up an account through the app and with only eight (it doesn't say eight or more) characters, I forgot the password. I tried resetting 3 times and each time the login said incorrect code."

Should you buy the Alen BreatheSmart 35i?

✅ Buy it if: You want a quiet, efficient air purifier with a comprehensive set of air quality monitoring features, or if you are looking to buy multiple units for schools, offices or commercial premises. The Alen BreatheSmart 35i offers some of the best smart features we have seen in an air purifier, and it is one of the handful of units that can be easily used within a much broader network of interconnected devices.

❌ Do not buy it if: You are looking for an air purifier for large spaces, or if you have small children and/or playful pets. The Alen BreatheSmart 35i is not powerful enough to effectively cover spaces larger than 500 square feet (46 square meters), and its ill-thought-out vents may increase the risk of damage to the purifier's internal structures by letting small items fall through their cracks.

If Alen BreatheSmart 35i is not for you

Want something more affordable? Consider the BlueAir Blue Pure 411i Max. This sleek air purifier is just as quiet, smart-enabled and efficient as the Alen BreatheSmart 35i, but it is cheaper by more than $100 and comes in a wider range of designs. However, its air quality monitoring features are not nearly as in-depth.

Looking for something more pet-friendly? Then you can't go wrong with the Levoit Vital 200S. This air purifier was designed with cat and dog owners in mind: it has a washable pre-filter, designated Pet mode and sturdy build, plus it comes with a host of smart features and costs less than $200.

Need something more powerful? The Molekule Air Pro is a great option here. This premium air purifier either matches or outperforms the Alen BreatheSmart 35i in terms of coverage, smart features and air quality monitoring, but it is also priced at a whopping $1,014.

Alen BreatheSmart 35i: How we tested

During our testing of the Alen BreatheSmart 35i air purifier, we spent nearly three months assessing its design, features, day-to-day performance, connectivity with third-party devices, ease of use and value for money. We checked the cost and availability of its air filter replacements and measured its noise levels using a Sound Meter decibel-counting app.

Moreover, we assessed its air-cleaning capabilities. We conducted a series of performance tests using a Perfect Prime air particle monitor, an industry-grade device that detects pollutants as small as 0.3 microns. We started with an ambient test, where we ran the Alen BreatheSmart 35i on its Auto mode for 15 and 30 minutes and recorded the change in air quality over time. Next, we smoke tests using where we burned matches and incense to simulate severe pollution. For each scenario, we recorded the air quality before and after running the purifier for 15 and 30 minutes on different settings.