It's the question we get asked most before anyone even requests a quote: "what power do I need?" The exact answer depends on your specific home, but there's a general industry rule of thumb that gets you a pretty solid estimate before you start looking at units.
The general rule: BTU per m²
As an orientative reference for the Mediterranean climate of the Vega Baja, the usual calculation is 450 to 600 BTU/h per m² of the room, assuming standard ceiling height (around 2.5 m) and average sun exposure. Here's the breakdown by room size:
| Room size | Orientative BTU/h | Typical example |
|---|---|---|
| Up to 10 m² | 5,000–7,000 | Small bedroom |
| 10–15 m² | 7,000–9,000 | Large bedroom, home office |
| 15–20 m² | 9,000–12,000 | Main bedroom, small living room |
| 20–30 m² | 12,000–16,000 | Medium living room |
| 30–40 m² | 16,000–20,000 | Large open living/dining room |
| 40–50 m² | 20,000–24,000 | Open-plan space, ground floor |
Keep in mind these are orientative ranges, not fixed figures — your actual home's result can sit within, or even outside, these margins depending on the factors below.
What pushes the real figure up or down
- Orientation and direct sun hours: a room facing south or west with direct afternoon sun needs more power than an equivalent north-facing room.
- Ceiling height: anything above the standard 2.5 m means more air volume to cool, even with the same floor area.
- Insulation and window quality: double glazing and good insulation reduce the heat load; an older property with single-pane aluminium windows increases it.
- Number and size of windows: more glazed surface means more heat gain during the day.
- Occupants and appliances: a kitchen with an oven and several appliances running, or a room that's regularly used by several people at once, generates extra heat the unit also has to offset.
What if my living room and kitchen are open-plan?
In homes with an open-plan living room and kitchen, the usual approach is to add up the total m² of the combined space and size the unit as one large room, not two separate ones. It's one of the cases most worth confirming during a technical visit, since the result changes quite a bit depending on where the sun comes in and how often the kitchen adds extra heat.
What happens if the unit has the wrong power
Both mistakes are equally common, and neither is free:
- Undersized unit (too little power): it will never bring the temperature down on the hottest days, no matter how well it's running mechanically. It's permanently forced to max output, which also shortens its lifespan.
- Oversized unit (too much power): it cools very quickly and shuts off, in short, constant on-off cycles. This not only wastes more electricity than necessary, it also dehumidifies less effectively, leaving an unpleasant "cold and damp" feeling.
This is also one of the reasons a badly sized unit can drive up electricity consumption — we cover it in more detail in our guide on how much electricity air conditioning uses and how to cut your bill.
Work out your exact case
This table gives you a quick reference, but for a result tailored to your actual home, try our free power calculator: in under a minute you get an estimate in BTU based on your m², orientation and location. And once you're ready to install, the free technical visit confirms the definitive figure on site, with no obligation.