One of the most important choices when buying an AC is the right capacity in kW. Too little and the AC runs flat out without ever really cooling the room. Too much and you waste money and get fluctuating temperatures. In this guide you'll calculate what you need.
The rule of thumb
For an average living space in the Netherlands:
100 watts of cooling capacity per square metre.
A living room of 30 m² therefore needs around 3,000 watts = 3.0 kW. This is a starting figure — several factors push it up or down.
Capacity per room size
| Room area | Recommended capacity | Typical use |
|---|---|---|
| 15 – 25 m² | 2.0 – 2.5 kW | Bedroom, small living room |
| 25 – 35 m² | 2.5 – 3.5 kW | Medium living room |
| 35 – 50 m² | 3.5 – 5.0 kW | Large living room, open kitchen |
| 50 – 70 m² | 5.0 – 7.0 kW | Loft, semi-open ground floor |
| 70+ m² | Multi-split recommended | Whole home or business space |
Factors that affect capacity
The rule of thumb is a starting point. Multiply it by the correct adjustment factor:
1. Ceiling height
The standard assumes a ceiling of 2.5 m. For every extra 0.5 m: +10% capacity. A room with a 3.5 m ceiling? Add 20%.
2. Insulation
- Energy label A+: -10% capacity
- Label B–C: standard value
- Label D or worse: +15–20% capacity
- Pre-war home without cavity wall: +25%
3. Sun exposure
- Many south- or west-facing windows: +20%
- Skylight(s) in the room: +15% per skylight
- Shaded side (north): -10%
4. Heat sources in the space
- Open kitchen with stove: +15%
- Lots of electronics (PC, TV, server): +10%
- Many people (office): +100 W per person
Calculation examples
Example 1: Bedroom 18 m² (label B, 2.5 m ceiling, north-facing)
18 × 100 = 1,800 W base, -10% north-facing = 1,620 W = 1.6 kW. A 2.0 kW AC is more than enough.
Example 2: Living room 40 m² (label C, 2.7 m ceiling, SW windows)
40 × 100 = 4,000 W base, +4% height, +20% windows = 4,960 W = 5.0 kW. Choose a 5.0 kW model.
Example 3: Pre-war apartment 28 m² (label D, skylight, SW)
28 × 100 = 2,800 W base, +25% insulation, +15% skylight, +20% sun = 4,480 W = 4.5 kW. Surprisingly high — not a 2.5 kW AC but at least 4.5 kW.
What if I also want to heat?
An AC that also heats (air-to-air heat pump) typically delivers 20–30% more capacity in heating mode than in cooling mode. A 3.5 kW AC therefore produces 4.5–5.0 kW of heat. So for winter heating you could go slightly smaller, provided your home is well-insulated.
Too big or too small: what happens?
Too small
- AC runs constantly at full power — high electricity bill
- Room doesn't get cool enough on hot days
- Faster compressor wear
Too big
- AC cools too fast, switches off, comes back on — fluctuating temperature
- Insufficient dehumidification (air feels clammy)
- Unnecessarily high purchase price and energy use
Tip: when in doubt go slightly largerrather than smaller. Modern inverter ACs can run at low speeds when less capacity is needed, so the penalty for "too big" is smaller than it used to be.
Let us calculate it
With every quote we do a professional heat-loss calculation — free of charge. We factor in the exact orientation of your windows, insulation level, glass area and use. So you'll never end up with an AC that's too small or too large.
Request a free survey or read on about the cost of an AC installation.