How much capacity do I need for 25 m²?
As a rough guide, between 2,000 and 3,000 kcal/h — but it depends on orientation, insulation and use. It is not an exact figure without knowing the actual property.
What air conditioning capacity does a home need?
Floor area is just the starting point. Here are the factors that really determine the capacity you need.
Guide
What air conditioning capacity does a home need?
The most common starting point is the wrong one: “I have X square metres — what capacity do I need?” Floor area matters, but it does not tell the whole story. Two homes of the same size in the same building can need very different systems depending on orientation, insulation and how the space is used.
Why floor area alone is not enough
Getting the capacity wrong has real consequences. An undersized unit will never reach the desired temperature on the hottest days: it runs continuously without achieving comfort. An oversized unit cools quickly and stops, with frequent start-stop cycles that are less efficient and put more strain on the compressor. It also fails to properly dehumidify the air, leaving a cool but clammy feeling.
The right capacity is the one that balances comfort, efficiency and longevity.
The factors that really matter
A proper capacity calculation considers several elements:
- Floor area and volume: Square metres are the starting point. Ceiling height also matters — a high ceiling means more air to condition.
- Solar orientation: A room facing south or west receives direct sunlight during the hottest hours and needs more cooling capacity than the same room facing north.
- Insulation: Good insulation significantly reduces demand. An older property with thin walls and single-glazed aluminium windows loses or gains heat much more easily.
- Glazed area: Large windows transmit a lot of heat. A living room with a south-facing glass wall needs far more capacity than the same space with a small window.
- Occupancy and equipment: People and electrical appliances generate heat. A continuously occupied office has higher demand than an empty room of the same size.
- Local climate: On the Costa Blanca, July and August set the design conditions. The peak summer temperatures determine the maximum demand.
Rough guidance — not an exact formula
As a general reference, residential spaces typically require between 100 and 130 W per square metre. Well-insulated homes with favourable orientation may need less; top-floor flats facing south with large windows or older buildings may need more.
An online calculator can give a useful starting estimate. It should never be used as the only basis for purchasing a unit — real property characteristics are essential for accurate sizing.
The risk of oversizing
A bigger unit is not always better. An oversized system cools rapidly then stops before completing its dehumidification cycle. The result can be a low temperature with high humidity — uncomfortable. The compressor also suffers more from frequent on-off cycles, reducing its working life.
Split, multi-split or ducted: implications for sizing
The system type also affects the approach to sizing:
- Individual split inverter: Each unit is sized for the specific room. The most common solution for flats and individual rooms.
- Multi-split: One outdoor unit feeds several indoor units. The combination of indoor units must not exceed the outdoor unit's capacity.
- Ducted system: A central unit distributes air to zones. Sizing requires calculating simultaneous demand across all spaces.
The site visit: the step that avoids costly mistakes
Before choosing a unit, the most practical step is to have a technician visit the property. In 20–30 minutes they can assess orientation, insulation, layout and intended use. With that information, sizing has a real basis and the quote is more accurate and reliable.
Avoid surprises after installation: a poorly sized unit is a mistake that stays with you for the life of the product.
Common questions
Frequently asked questions
Is it safer to oversize for peace of mind?
No. Oversizing causes short cycling, lower energy efficiency and poor dehumidification. The goal is correct sizing based on the real property.
Do inverter units consume less?
Yes. They modulate output to match actual demand, reducing consumption and on-off cycling compared to fixed-speed units.
How many splits do I need for a 3-bedroom flat?
It depends on size, layout and whether rooms are used simultaneously. Sometimes a multi-split covers everything; other times independent units per room work better.
Why is my unit not cooling well if it has enough capacity?
Possible causes include dirty filters, refrigerant loss or an installation issue. A technical inspection will identify the problem.
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