Alen BreatheSmart 75i
#12 in Large roomsFull review
A premium large-room purifier with long-lasting filters, for buyers willing to pay for quiet and a subscription-backed guarantee.
Amazon $699.59$699.59
The Alen BreatheSmart 75i is the better air purifier overall, rated 3.3 to 2.7. The Alen BreatheSmart 75i leads on filter cost, auto mode and efficiency. The AirDoctor AD4000 costs $20.59 less ($679 vs $699.59).
AirDoctor AD4000
#15 in Large roomsFull review
A large-room purifier with strong certified CADR and odor filtration, but high filter costs.
Amazon $679$679
Prices were last checked October 22, 2026 and are subject to change; the price and availability shown by the retailer at the time of purchase apply.
Which should you buy?
- Choose the Alen BreatheSmart 75i for filter cost ($99 a year in filters vs $239.90 a year in filters), auto mode (particle sensor and Wi-Fi app vs PM2.5 sensor, auto mode) and efficiency (6.9 cfm per watt vs 5.6 cfm per watt).
Scores side by side
Each factor is scored 0-100 against the same fixed reference points for every large rooms air purifier; a clear win is highlighted. How we rank explains each one.
| Factor weight | Alen BreatheSmart 75i | AirDoctor AD4000 |
|---|---|---|
| Overall rating | 3.3/5 | 2.7/5 |
| Value 25% | 0 $1.89 per cfm of smoke CADR | 0 $1.84 per cfm of smoke CADR |
| Filter cost 20% | 76 $99 a year in filters | 22 $239.90 a year in filters |
| Quiet 20% | 60 51 dB at top speed (maker rating) | 50 noise at top speed not published (neutral score used) |
| Efficiency 15% | 61 6.9 cfm per watt | 45 5.6 cfm per watt |
| Auto mode 10% | 100 particle sensor and Wi-Fi app | 70 PM2.5 sensor, auto mode |
| Warranty 10% | 50 warranty not published (neutral score used) | 50 warranty not published (neutral score used) |
Specifications
| Alen BreatheSmart 75i | AirDoctor AD4000 | |
|---|---|---|
| Performance | ||
| Smoke CADR | 370 cfm | 370 cfm |
| Dust CADR | 351 cfm | 393 cfm |
| Pollen CADR | 431 cfm | 450 cfm |
| PM2.5 CADR | 360 cfm | 381 cfm |
| CADR certified by | ENERGY STAR | ENERGY STAR |
| Room size (AHAM) | 574 sq ft | 574 sq ft |
| Coverage (maker) | 2,800 sq ft | 2,776 sq ft |
| Noise | 25 to 51 dB | - |
| Efficiency | ||
| Efficiency (IEF) | 6.9 cfm/W | 5.6 cfm/W |
| ENERGY STAR | Yes | Yes |
| Energy use | 304 kWh/year | 396.2 kWh/year |
| Power at top speed | 55 W | - |
| Filters | ||
| Filter | HEPA (Essential/Pure filter as sold in this listing) | UltraHEPA with carbon/VOC filter and pre-filter (single filter unit) |
| Activated carbon | No | Yes |
| Replacement | Essential (Pure), formerly B7 | AD4000 filter unit |
| Replacement cost | $99 every 12 months | $119.95 every 6 months |
| Yearly filter cost | $99/year | $239.90/year |
| Ionizer | Yes, can be switched off | - |
| CARB certified (ozone) | Yes | Yes |
| Controls and build | ||
| Air-quality sensor | particle | PM2.5 |
| Auto mode | Yes | Yes |
| Wi-Fi app | Yes | - |
| Fan speeds | 5 | 6 |
| Dimensions | 27 x 18.5 x 11.5 in | - |
| Weight | 27 lb | 15.8 lb |