TL;DR — Buy for the room, not the house. One oversized purifier in the bedroom beats three small ones scattered around.
Most air purifier disappointment comes from one mistake: buying a unit rated for a large room and expecting it to clean an entire floor.
Sizing: the only number that matters
CADR (Clean Air Delivery Rate) tells you how much clean air a unit delivers per minute. A rough rule for allergy sufferers:
Required CADR (m³/h) ≈ room area (m²) × ceiling height (m) × 5That ”× 5” assumes you want five air changes per hour, which is what allergy guidance generally recommends. A 20 m² bedroom with 2.5 m ceilings needs about 250 m³/h of CADR.
| Room | Area | Recommended CADR | Typical noise on high |
|---|---|---|---|
| Bedroom | 15–20 m² | 200–250 m³/h | Under 45 dB |
| Living room | 30–40 m² | 450–600 m³/h | 50–58 dB |
| Home office | 10–12 m² | 150–180 m³/h | Under 40 dB |
1. Best for bedrooms — Placeholder Pure Sleep
- CADR: placeholder — 240 m³/h
- Noise on low: 22 dB (effectively silent)
- Filter life: 12 months, replacement cost placeholder
- Extras: true HEPA H13 + activated carbon layer, display auto-dims
2. Best for large rooms — Placeholder Pure Max
- CADR: placeholder — 600 m³/h
- Noise on high: 55 dB — noticeable, so run it high while out, low while home
- Filter cost: higher; budget for two changes a year
What actually helps allergy symptoms
- True HEPA (H13 or H14) — “HEPA-like” and “HEPA-type” filters are not the same thing
- Run it continuously on low rather than in bursts on high
- Replace filters on schedule — a saturated filter stops capturing particles
- Keep windows closed on high-pollen days; purifiers cannot keep up with an open window
- Bedroom first — you spend eight hours breathing that air
Features you can skip
- Ionisers (limited benefit, some produce ozone)
- “Smart” air quality scores that are not calibrated
- UV-C lights — residence time in most units is too short to matter
Editorial note. This guide is compiled from official product documentation and practical buying checklists, not hands-on testing. Verify specifications and current pricing with the manufacturer before you buy. See our affiliate disclosure for how we fund this work.
