Sizing air conditioning to a room

Start with floor area

Floor area gives the starting figure. As a working rule we design to these bands, then adjust for the things that actually change the load.

• Up to 20 m² — 2.5 kW (9,000 BTU)
• 20–35 m² — 3.5 kW (12,000 BTU)
• 35–50 m² — 5.0 kW (18,000 BTU)
• 50–70 m² — 7.0 kW (24,000 BTU)

Then adjust for the room itself

Two rooms of the same size can need different equipment. A south-facing lounge with full-height glazing gains far more heat than a shaded north-facing bedroom, and a loft conversion under an uninsulated roof behaves differently again.

• Full sun or large glazing — step up one band
• Heavily shaded, well-insulated room — the lower band is usually enough
• Ceilings above 2.7m — add roughly 10% to the load
• Kitchens, server rooms and shops — add for appliance and people gain

Why oversizing is a mistake

An oversized inverter unit reaches setpoint quickly, then short-cycles. You get temperature swings, poorer dehumidification, more noise and shorter compressor life — for a higher purchase price. Slightly undersized is uncomfortable in a heatwave; heavily oversized is uncomfortable all year.

What we do with your answers

The quote builder asks for room type, size band, sun load and ceiling height, then recommends a kW per room. You can override it — the figure is a recommendation, not a lock — and anything unusual gets checked on survey before the price is confirmed.