Yawnder buying guide · Manufacturer information checked October 2026
Quick take
75i: Start here for more particle-cleaning capacity and a larger room. 45i: Consider it when you want a smaller model with a particle sensor and automatic mode. FLEX: Compare it for a simpler manually controlled option; Alen’s support page says it has no built-in particle sensor or automatic speed adjustment.
Choose by the clean air delivery rate (CADR) for your room, the noise at a usable fan speed and ongoing filter cost. This is a research-based buying guide, not a new head-to-head Yawnder laboratory test. Availability and specifications vary by model version.
Check current Alen models and pricing
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Alen 75i vs 45i vs FLEX
| Feature | BreatheSmart 75i | BreatheSmart 45i | BreatheSmart FLEX |
|---|---|---|---|
| Particle-cleaning capacity | Highest of these three in Alen’s published figures. | Middle option; verify the exact version’s CADR. | Alen support lists CADR 225; verify the unit and current availability. |
| Particle sensor / auto mode | Yes, according to Alen support. | Yes, according to Alen support. | No built-in particle sensor or auto speed, according to Alen support. |
| App | Supported; Wi-Fi requirements vary by version. | Supported; Wi-Fi requirements vary by version. | Alen does not list FLEX as a supported purifier in its app FAQ. |
| Filter | Different 75i filter sizes and options. | Shares compatible filter family with FLEX. | Shares compatible filter family with 45i. |
| Best reason to consider | More capacity for a larger room or higher cleaning rate. | Automatic operation without the 75i’s size. | A simpler control setup if an automatic sensor is not important. |
These are manufacturer descriptions, not Yawnder-measured results. Confirm the exact version, filter and controls before ordering.
Size the purifier for your room
Measure the length and width of the space, then compare the room area with the purifier’s particle CADR. The EPA’s approximate sizing table uses an 8-foot ceiling: a 200-square-foot room calls for a smoke CADR of about 130 cfm, a 400-square-foot room about 260 cfm, and a 600-square-foot room about 390 cfm. Higher ceilings or an open layout may require more capacity or multiple units.
Alen’s square-foot figures can look much larger because its pages describe different cleaning intervals, such as once per hour versus once every 30 minutes, at the highest speed. They are not interchangeable with an EPA room-sizing estimate. A purifier run on a quieter, lower speed cleans less air per minute than its maximum-speed CADR suggests.
Alen’s own pages do not currently agree on every figure: its 75i product page lists CADR 375 while its support page lists 347; the 45i product and support pages list 255 and 245 respectively. Versions or page updates may differ. Use the label or documentation for the exact unit you intend to buy, and allow extra capacity if you plan to use a lower setting.
Which model should you choose?
75i: more capacity
Compare the 75i for a larger bedroom, living room or open space where you want more clean air delivery. Its size, purchase price and replacement filters can be greater commitments. Check where it will sit and whether a lower fan speed is still sufficient for the room.
45i: automatic operation
The 45i has a particle sensor and automatic mode in Alen’s support information. It is a practical middle choice when you want the fan to respond to changes in detected particles. Sensor readings and auto settings do not measure every pollutant; check the exact model version and Wi-Fi requirements if app control matters.
FLEX: manual controls
FLEX is a simpler model without a built-in particle sensor or automatic fan control according to Alen. It may fit someone who prefers choosing the speed manually. Confirm availability and compare it with newer Alen models before treating it as the least expensive option.
Filters, smoke and odors
A particle filter can capture particles passing through the purifier, including dust, pollen and some smoke particles. The percentage printed on a filter is not the same as the percentage removed from all the air in a room. Use the unit’s CADR, room size and operating speed to compare particle cleaning.
Odors and gases are a separate issue. Some replacement filters include activated carbon, but carbon amount and contact time matter; a particle CADR does not measure gas removal. For cooking smoke or wildfire smoke, address the source and ventilation as appropriate as well as filtering particles. A purifier is not a substitute for a carbon monoxide alarm.
Alen lists different filter choices and replacement schedules. The 45i and FLEX share a compatible filter family; the 75i uses its own. Price out the exact replacement filter and shipping, check the recommended interval, and remember actual filter life depends on use and air quality.
Noise, sensors and ozone
Compare noise at the speed you will actually use, not just the quietest advertised setting. If the purifier must run fast enough for a bedroom, test whether the sound is acceptable while sleeping. Automatic mode can turn the fan up when a sensor detects particles, which may be useful but can also be noticeable at night.
Alen lists an optional ionizer on some models and says the FLEX has none. EPA recommends avoiding air cleaners that intentionally produce ozone in occupied spaces. Check the exact model and instructions; if an ionizer is optional, keep it off if you want mechanical filtration without that feature.
Price, filter costs and warranty
Compare the purifier, chosen filter, replacement schedule and shipping rather than the unit price alone. Alen’s support page lists filter-life estimates based on continuous operation; a smoky or dusty environment can change replacement needs. Features, discounts and prices can change, so check the current listing.
Read the warranty terms for your purchase. Alen’s FLEX support page describes its Forever Guarantee as requiring product registration and an active filter subscription. Confirm the conditions, exclusions and applicable version before relying on the warranty.
Frequently asked questions
Does the FLEX have an air-quality sensor?
Alen’s FLEX support documentation says it has no built-in particle sensor or automatic speed mode. Check the exact model and version.
Does a HEPA purifier remove carbon dioxide?
A typical particle filter is not a solution for elevated CO₂. Fresh-air ventilation addresses CO₂ buildup; an air purifier can complement ventilation by reducing airborne particles.
Is the largest model always the best?
No. Match clean-air delivery to the room and the fan speed you can tolerate, then consider space, filter costs and controls. Extra capacity can be useful if you want to run the fan more quietly.
Can I try these in the Yawnder showroom?
Availability changes. Contact the Encinitas showroom before visiting to ask whether specific air purifiers are on display.