Blueair Blue Signature Large (SP4i) vs Windmill Windmill Air Purifier (975 sq ft model)
Blueair Blue Signature Large (SP4i)
Windmill Windmill Air Purifier (975 sq ft model)
The short answer
Blueair Blue Signature Large (SP4i) comes out ahead overall with 7.8/10 against 6.8/10 for the Windmill Windmill Air Purifier (975 sq ft model). Blueair Blue Signature Large (SP4i) is stronger on noise at sleep-usable speeds, cleaning performance for bedroom size and running cost & ownership. Windmill Windmill Air Purifier (975 sq ft model) is stronger on sleep-friendly features and indoor-air safety & materials. At current verified prices, the Windmill Windmill Air Purifier (975 sq ft model) costs about $240.99 less.
- Choose the Blueair Blue Signature Large (SP4i) if: Light sleepers with a large primary bedroom who will pay for the most quiet airflow and accept an always-on ionizer.
- Choose the Windmill Windmill Air Purifier (975 sq ft model) if: Sleepers who want built-in white noise and a minimalist design for a small bedroom.
Scores by criterion
| Criterion | Blueair Blue Signature Large (SP4i) | Windmill Windmill Air Purifier (975 sq ft model) |
|---|---|---|
| Noise at sleep-usable speeds | 9.3HouseFresh: 229 cfm at 40 dB, 34.8 dB in sleep mode. | 7.5Tom's Guide: 38.4 dBA on low. |
| Cleaning performance for bedroom size | 9.0455 smoke CADR rated; 229 cfm measured at a quiet 40 dB. | 5.0130 cfm, 202 sq ft. |
| Sleep-friendly features | 8.3Night mode, laser PM2.5 sensor, app. | 8.8Whisper mode with lights off, White Noise mode, app. |
| Indoor-air safety & materials | 5.0Ionizer cannot be switched off (HouseFresh). | 8.0No ionizer; AHAM Verifide, CARB, Energy Star listed. |
| Running cost & ownership | 5.5About $180 a year in filters (HouseFresh). | 5.0Proprietary 6-month filters. |
| Value | 5.8$439.99 on Amazon. | 6.0$189 from a third-party seller on Amazon. |
Specifications
| Spec | Blueair Blue Signature Large (SP4i) | Windmill Windmill Air Purifier (975 sq ft model) |
|---|---|---|
| Lowest-speed noise (manufacturer) | 23 dB | 16 dB |
| Top-speed noise (manufacturer) | 55 dB | 52 dB |
| Lowest-speed noise (independent measurement) | 34.8 dBA | 38.4 dBA |
| CADR (smoke where given, else headline) | 455 cfm | 130 cfm |
| Recommended room size (4.8–5 ACH / AHAM) | 705 sq ft | 202 sq ft |
| Sleep / night mode | Yes | Yes |
| App control | Yes | Yes |
| Ionizer / electrostatic stage | Ionizer that cannot be disabled (per HouseFresh) | None mentioned |
| Filter type | 7-stage filter incl. pelleted carbon | 3-in-1 H13 HEPA with activated carbon layer (proprietary) |
| Main filter life | — | 6 months |
Blueair Blue Signature Large (SP4i)
Pros
- 34.8 dB in sleep mode
- About 229 cfm at 40 dB
- Large coverage
- App control and PM2.5 sensor
- Doubles as a side table
Cons
- Ionizer cannot be turned off
- Premium price
- About $180 a year in filters
- Tabletop surface scratches easily
The quietest high-airflow option for a big room, but only for buyers who accept the always-on ionizer and the cost.
Full Blueair Blue Signature Large (SP4i) review →Windmill Windmill Air Purifier (975 sq ft model)
Pros
- White Noise mode
- Lights-off Whisper mode
- Minimalist design
- App control
- Multiple certifications listed
Cons
- Modest 130 cfm CADR
- Filters every six months
- Among the costliest to own
- Amazon offer is third-party
A design and sleep-sound pick, not a performance pick. Buy it for the look and the white noise.
Full Windmill Windmill Air Purifier (975 sq ft model) review →Both products are part of our guide The Best Quiet Air Purifiers for Bedrooms of 2026, where you can see every pick, how we score and current prices from each retailer.