Alen BreatheSmart 35i

What Is the Alen BreatheSmart 35i?

The Alen BreatheSmart 35i is a compact HEPA air purifier built for small to medium rooms, handling spaces up to 1,400 square feet with one full air cycle per hour, or 700 square feet if you want two cycles an hour for faster results. It sits at the entry point of Alen’s smart purifier lineup, priced at $289, which makes it the most affordable model that still comes loaded with app connectivity and smart sensor tech.

This isn’t a stripped-down bargain unit, though. The 35i packs in a laser sensor that tracks PM 2.5, TVOC, eCO2, temperature, and humidity, then automatically adjusts fan speed based on what it finds. It’s also Quiet Mark Certified, Asthma & Allergy Friendly certified, SleepScore Validated, and carries a Mom’s Choice award, which gives it a fairly well-rounded resume for a unit in this price bracket.

Key Features Worth Knowing About

Filtration Options

Alen offers three filter tiers for the 35i, and picking the right one matters more than people expect. The Essential (Pure) filter is the entry-level option, running $54 and lasting 9 to 12 months with constant use. It captures 99.9% of airborne particles down to 0.1 microns, including dust, viruses, and allergens, which covers most basic air quality concerns.

Step up to Advanced (Fresh) and you get the same HEPA base plus a carbon layer aimed at asthma triggers, chemicals, VOCs, and smoke. The Ultimate (Odor) filter goes even further with a proprietary carbon catalyst blend designed for odor, mold, and pet-heavy households. Both upgraded filters have a shorter lifespan of 6 to 8 months, so there’s a real tradeoff between filtration power and replacement frequency. If you’re dealing with pets, cooking odors, or smoke exposure, the extra filter cost is probably worth it.

Noise and Energy Use

One of the more practical selling points here is how quiet this thing runs. At its lowest speed it sits at 23 dB, which is close to silent, and even at the highest turbo setting it only hits 42 dB. That’s quieter than a normal conversation, and it’s part of why the unit earned its Quiet Mark Certification as one of the quietest 20% of air purifiers on the market. For a bedroom or home office where background noise actually matters, this is a meaningful difference from purifiers that hum loudly at night.

Power draw is equally modest, ranging from 0.9 to 35 watts depending on speed. That’s low enough to run continuously without worrying about your electric bill, and it’s part of why the unit has earned Energy Star recognition, including a spot on the 2025 Most Efficient list.

Smart Features and App Control

The 35i connects through the Alen Air app, which lets you monitor air quality in real time, control multiple units from one interface, set schedules, and get alerts. The filters themselves use RFID chips that communicate with the purifier to track remaining filter life, so you’re not left guessing when a replacement is due. The unit also supports over-the-air firmware updates, meaning new features can show up without buying new hardware.

There’s also an Auto Light Mode that dims the control panel based on ambient lighting, which is a small touch but a nice one if you’re running this in a bedroom overnight. The color-changing ring gives a quick visual read on air quality without needing to pull out your phone.

Photo: Alen

Pricing and Value

At $289, the 35i lands as the budget entry point into Alen’s smart purifier range, compared to $799 for the largest model and $449 for the mid-tier option. Given that it still includes app control, automatic speed adjustment, and the same certifications as pricier models, it’s a reasonable value if your space fits within its coverage range.

The ongoing cost is filters, running $54 for the Essential tier and lasting the better part of a year. Alen backs the unit with a Forever Guarantee, meaning they’ll repair or replace it for free if something goes wrong, but only if you’ve registered the product and maintain an active filter subscription. That subscription also knocks 10% off replacement filters, which helps offset the recurring cost over time.

Who Should Buy This, and Who Shouldn’t

This purifier makes the most sense for people furnishing a bedroom, home office, nursery, dorm, or studio apartment. Its 700 to 1,400 square foot range covers most single rooms and smaller open layouts comfortably, and the low noise profile means it won’t interrupt sleep or focus work. Pet owners and allergy sufferers get extra mileage out of the higher-tier filters, since the HEPA base captures dander and dust at a 99.9% rate.

If you’re trying to cover a large open-concept kitchen and living room, or anything approaching 2,000+ square feet, this isn’t the right model. Alen’s larger units are built specifically for that kind of coverage with higher CADR ratings. Similarly, if you want an ionizer function, the 35i doesn’t include one, so anyone specifically shopping for ionization will need to look at Alen’s other models instead.

Photo: Alen

Bottom Line

The Alen BreatheSmart 35i is a well-rounded, quiet, and energy-efficient air purifier that earns its smart-purifier label without the smart-purifier price tag. The filtration options let you scale up protection depending on your household’s specific needs, whether that’s basic dust and allergen control or more aggressive odor and VOC filtration. App control, filter tracking, and a Forever Guarantee add long-term value that’s easy to overlook when just comparing sticker prices.

Where it falls short is coverage for larger spaces and the absence of an ionizer, both of which push buyers with bigger rooms or specific filtration preferences toward Alen’s pricier models. For anyone furnishing a single room, though, the 35i hits a sensible balance of price, quiet operation, and smart features. The question worth sitting with is simple: how much are you actually willing to pay in ongoing filter costs for cleaner air over the next several years?

Frequently Asked Questions

How many fan speeds does the 35i have?

It comes with four fan speeds, starting at a whisper-quiet 23 dB and topping out at 42 dB on turbo. That range gives you flexibility between near-silent overnight use and faster air cycling during the day.

How often do I need to replace the filter?

The Essential filter lasts 9 to 12 months under recommended 24/7 use, while the Advanced and Ultimate filters last 6 to 8 months. The app and RFID-equipped filters track usage and alert you when it’s time for a swap.

Does the 35i work with pets in the home?

Yes, especially with the Ultimate (Odor) filter, which includes a carbon catalyst blend built for pet-filled homes. The HEPA base across all filter tiers also captures pet dander at a 99.9% rate for particles as small as 0.1 microns.

Is the BreatheSmart 35i energy efficient?

It uses between 0.9 and 35 watts depending on fan speed, which is low enough for continuous operation without a noticeable impact on your electric bill. It also holds Energy Star certification, including a spot on the 2025 Most Efficient list.

What is the Forever Guarantee?

It’s Alen’s commitment to repair or replace your unit for free if something breaks, as long as you’ve registered the product and keep an active filter subscription. It’s a long-term value add that effectively removes the risk of the purifier failing outside a standard warranty window.

Can I control multiple units from one app?

Yes, the Alen Air app lets you manage several 35i units at once, including scheduling, air quality alerts, and filter tracking for each one individually. This is useful if you’re outfitting more than one room in your home.

Does it have an ionizer?

No, the 35i does not include an ionizer function, unlike some of Alen’s larger models. If ionization is a must-have for you, you’ll need to look at a different unit in the lineup.

How large of a space can it actually cover?

It purifies up to 1,400 square feet with one air cycle per hour, or 700 square feet if you want two cycles per hour for quicker results. That makes it well suited to bedrooms, offices, nurseries, and smaller apartments rather than large open floor plans.