What Cooling Load Do I Need?

Quick Sizing Guide

• Bedroom (15m²): ~1.0–1.2 kW (3,400–4,100 BTU)
• Living room (25m²): ~1.5–2.0 kW (5,100–6,800 BTU)
• Home office (12m²): ~1.0–1.5 kW (3,400–5,100 BTU)
• Office (per person): ~100–150W sensible heat gain
• Server room: Size to equipment heat output

Cooling Load by Room Type (W/m²)

• Domestic (normal glazing): 50–80 W/m²
• Domestic (large south-facing windows): 80–120 W/m²
• Office (standard): 80–120 W/m²
• Retail: 80–150 W/m²
• Restaurant: 120–200 W/m²
• IT/server room: 200–500+ W/m²

Factors That Increase Cooling Load

• Solar gain: South and west-facing windows are the biggest contributor in the UK
• Internal heat: People (~100W each), computers (~150W each), lighting
• Poor insulation: Heat conducts through walls and roof
• Top floor rooms: Heat rises and roof solar gain adds load
• Large glazing areas: Conservatories, floor-to-ceiling windows

Practical Example

A 20m² south-facing home office with large windows:

• Base load: 20 × 80 = 1,600W
• Solar gain (large windows): add 500W
• 2 people + computers: add 500W
• Total: approximately 2.6 kW
• Choose a unit rated 3.5 kW (next size up for headroom)

Cooling Options for the UK

• Split system air conditioning: Most efficient. 2.5–7 kW domestic units
• Portable air conditioning: No installation but less efficient and noisy
• Heat pump (reversible): Heating + cooling in one unit. Growing in popularity
• Evaporative cooler: Only effective in dry conditions (limited UK use)

Running Costs

A typical 3.5 kW split system uses ~1.0–1.2 kW of electricity (SEER ~3.5). Running 8 hours per day costs approximately £2.50–3.00 per day at current UK electricity rates (~£0.30/kWh).