Clean Air Hub
ACH Quick Reference Card
Air Changes per Hour Recommendations & CADR Sizing Guide
Residential ACH Recommendations
| Room | ACH | Priority |
|---|---|---|
| Bedroom | 4-6 | Sleep quality, allergen control |
| Living Room | 4-5 | General comfort, dust reduction |
| Kitchen | 6-8 | Cooking particles, odors |
| Bathroom | 6-8 | Humidity, mold prevention |
| Home Office | 4-6 | Focus, productivity |
| Nursery | 5-6 | Infant health, quiet operation |
| Gym/Workout | 6-8 | Heavy breathing, CO2 |
| Basement | 4-6 | Mold, radon mitigation |
Medical/Commercial Standards
| Setting | Min ACH |
|---|---|
| Hospital Ward | 6+ |
| Operating Theatre | 15-25 |
| Isolation Room | 12+ |
| Dental Office | 6-12 |
| GP Surgery | 6+ |
Source: NHS HTM 03-01, ASHRAE
The ACH Formula
ACH = (CADR × 60) ÷ Room Volume
Room Volume = Length × Width × Ceiling Height (in metres)
Quick Sizing Rule:
For 5 ACH with 2.4m ceiling: CADR needed = Room Area (m²) × 12
Example: 20m² room needs 240 m³/h CADR for 5 air changes per hour
CADR Quick Reference Table (2.4m ceiling)
| Room Size | CADR for 5 ACH | CADR for 6 ACH |
|---|---|---|
| 10m² | 120 m³/h | 144 m³/h |
| 15m² | 180 m³/h | 216 m³/h |
| 20m² | 240 m³/h | 288 m³/h |
| 25m² | 300 m³/h | 360 m³/h |
| 30m² | 360 m³/h | 432 m³/h |
| 40m² | 480 m³/h | 576 m³/h |
| 50m² | 600 m³/h | 720 m³/h |
When to Increase ACH
- • Allergy or asthma sufferers present
- • During cold/flu season
- • High outdoor pollution days
- • Pets in the home
- • Recent renovation or new furniture
Common Mistakes
- • Using manufacturer's max room rating (often 1 ACH)
- • Not accounting for open plan layouts
- • Ignoring ceiling height variations
- • Running purifier on low speed 24/7
- • Placing purifier in corner or behind furniture
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Free ACH Calculator: cleanair.app/calculator
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