What Air Change Rate Do I Need?

Recommended Air Change Rates

• Living room: 0.5–1.0 ACH
• Bedroom: 0.5–1.0 ACH
• Kitchen: 1.0–1.5 ACH (continuous), higher when cooking
• Bathroom: 1.0–1.5 ACH (continuous), higher when bathing
• Utility room: 1.0–1.5 ACH
• WC: 1.5–2.0 ACH

How to Calculate Ventilation Rate

To convert ACH to litres per second (l/s):

• Room volume = Length × Width × Height (m³)
• Example: 4m × 3m × 2.4m = 28.8m³
• At 1.0 ACH: 28.8m³/hr = 8 l/s (divide by 3.6)

Building Regulations (Approved Document F)

Part F specifies minimum ventilation rates in two ways:

• Whole-dwelling rate: Based on number of bedrooms and occupants
• Room-by-room extract rates: Specific l/s values for wet rooms

For a typical 3-bed house, the whole-dwelling ventilation rate is approximately31 l/s (based on 0.3 l/s per m² floor area).

Why Air Change Rate Matters

• Too low: Condensation, mould growth, poor air quality, health risks
• Too high: Wasted energy, draughts, uncomfortable temperature
• Right balance: Good air quality, moisture control, energy efficiency

Modern airtight homes (post-2021 Building Regs) need mechanical ventilation because they do not have enough natural air leakage to maintain healthy indoor air quality.