Complete Guide 2026
What Air Conditioner to Buy by m² or Room Size
Calculate the cooling capacity you need, avoid the most common mistakes and choose the right unit for your space with our updated 2026 guide.
🧮 Cooling capacity table by m²
⚡ Inverter technology
✓️ Mistakes to avoid
Not sure what air conditioner to buy based on the square metres of your room or living area? Choosing a unit with the wrong capacity is the most common and most costly mistake: a unit with too few frigories will never cool properly and will run at full power all day long; an oversized one will short-cycle constantly without dehumidifying the air. In this complete 2026 guide we explain how to calculate the cooling capacity you need based on m², the correction factors that adjust the calculation, the types of units available and everything you need to know before buying.
Table of contents
- What capacity do I need by m²? The definitive table
- What are frigories and how are they calculated?
- Factors that modify the calculation
- Types of air conditioner: which one suits you
- Energy label and Inverter technology
- Most common mistakes when buying
- Installation and maintenance tips
- Frequently asked questions
1What capacity do I need by m²? The definitive table
The table below gives the indicative cooling capacity by square metres, based on the industry standard rule of 100 frigories per square metre at a standard ceiling height of 2.5 m:
| Floor area | Frigories | Capacity (kW) | BTU | Typical use |
|---|---|---|---|---|
| Up to 20 m² | 2,000 – 2,500 | 2.0 – 2.9 kW | ~9,000 | Small bedroom, studio |
| 20 – 30 m² | 2,500 – 3,000 | 2.9 – 3.5 kW | ~12,000 | Double bedroom, office |
| 30 – 50 m² | 3,000 – 5,000 | 3.5 – 5.8 kW | ~18,000 | Medium living room, small flat |
| 50 – 70 m² | 5,000 – 7,000 | 5.8 – 8.1 kW | ~24,000 | Large living room, medium flat |
| 70 – 90 m² | 7,000 – 9,000 | 8.1 – 10.5 kW | ~30,000 | Large flat, ground floor |
| 90 – 120 m² | 9,000 – 12,000 | 10.5 – 14.0 kW | ~36,000 | Large house, commercial premises |
| Over 120 m² | +12,000 | +14.0 kW | +48,000 | Consult a professional installer |
⚠️ Important: This table is indicative only. Factors such as climate zone, insulation or orientation can shift the result by 15–30%. Always consult a certified installer for a definitive calculation.
📋 Regulatory note: If the unit exceeds 4,500 frigories (5 kW thermal), it must be registered with the regional Industry authority and installation must be carried out by an F-Gas certified technician.
2What are frigories and how are they calculated?
Before looking at any catalogue, it is essential to understand the three units you will see in every technical data sheet:
Frigories (kcal/h) — the measure of cooling
- What it is: A frigoría measures the heat the unit extracts from the room per hour. It is the most widely used refrigeration unit in Spain.
- Quick rule: 100 frigories per m² at a standard ceiling height of 2.5 m.
- Conversion: 1 frigoría = 1.163 W. For example, 2,000 frigories = 2,326 W = 2.3 kW.
Watts and kW — thermal capacity
- What it is: kW measure the thermal capacity of the unit, i.e. its ability to cool or heat.
- ⚠️ Do not confuse: Thermal capacity (cooling output) is very different from electrical consumption. A 3.5 kW thermal unit may consume only 1 kW of electricity thanks to Inverter technology.
- Conversion: To convert kW to frigories, multiply by 860. A 3.5 kW unit = 3,010 frigories.
BTU — the unit you will see in catalogues
- What it is: BTU (British Thermal Unit) are used in many technical data sheets for Asian-manufactured equipment and in international comparisons.
- Quick conversion: 1 frigoría = 4 BTU. A 9,000 BTU unit equals 2,250 frigories.
- Most common models: 9,000 BTU (~2,250 frig.), 12,000 BTU (~3,000 frig.), 18,000 BTU (~4,500 frig.), 24,000 BTU (~6,000 frig.).
✓️ Quick formula: m² × 100 = frigories needed. For high ceilings (over 2.7 m), use: m³ × 50 = frigories.
3Factors that modify the cooling capacity calculation
The 100 frigories per m² rule is just the starting point. These factors can increase the required capacity by 15–30%:
Orientation and solar exposure
- South or south-west facing: Add 15–20% to the calculated frigories.
- Top-floor flats and attics: Add 15–20%. An uninsulated roof absorbs solar heat all day long.
- Large windows or floor-to-ceiling glazing: Add 10–15% for each wall where more than 40% of the surface is glazed.
- Ground-floor units in shade: You can reduce the calculated capacity by 5–10%.
Climate zone (very important in Spain)
- Zone A (Canary Islands, southern Mediterranean coast): Add 20–25%. Extreme summer temperatures.
- Zone B (Seville, Córdoba, inland Andalusia): Add 15–20%. Very hot, long summers.
- Zone C (Madrid, Valencia, Barcelona): Apply the standard table with no correction.
- Zones D and E (northern Spain, Pyrenees): You can reduce by 10%. Milder, shorter summers.
Building insulation
- Old building (built before 1980) without renovation: Add 15–20%. Poor insulation allows far more heat to enter.
- Renovated building or built after 2006: Apply the standard table. The Spanish Building Code (CTE) requires minimum insulation levels.
- Passive house or energy certificate A/B: You can reduce by 10–15%.
People and internal heat sources
- Each regular additional occupant: Add 100 W (86 frigories) to the calculation.
- Kitchen or area with appliances: Add 1 kW (860 frigories) extra.
- IT equipment or servers: Add their full rated power to the thermal calculation.
- Tip: For living rooms regularly used by 4–6 people, add at least 500 frigories to the table result.
4Types of air conditioner: which one suits you
Once you have calculated the required capacity, the next step is to choose the right type of unit for your space:
1×1 Split — the most common option
- What it is: One indoor unit and one outdoor unit. The most widely installed system in Spain for domestic use.
- ✔ Ideal for: a single bedroom or living room up to 50 m²
- ✔ Efficient, quiet and straightforward to install
- ✘ Limitation: only conditions one room per outdoor unit
Multi-split — several rooms, one outdoor unit
- What it is: One outdoor unit connected to 2, 3 or more indoor units in different rooms.
- ✔ Ideal for: whole flats, homes of 70–120 m²
- ✔ Only one outdoor machine, independent control per room
- ✘ Limitation: if the outdoor unit fails, the whole system stops
Ducted system — central air conditioning
- What it is: A centralised system that distributes conditioned air throughout the home via ducts hidden in the ceiling.
- ✔ Ideal for: new builds or major renovations, over 100 m²
- ✔ Invisible, conditions the whole home, very even comfort
- ✘ Limitation: requires building work or pre-installed ductwork
Portable — no installation required
- What it is: A self-contained unit requiring no building work. Expels heat via a hose to the outside.
- ✔ Ideal for: temporary solution, rented properties, spaces up to 25 m²
- ✘ Less efficient, noisier and takes up floor space
- Tip: Only recommended if you cannot install an outdoor unit. For regular use, a split unit is always a better option.
5Energy label and Inverter technology: what to check before buying
The new energy label (A–G scale)
- New scale since 2021: Runs from A to G. The old A+++ ratings were rescaled; many units dropped to B or C under the new system.
- What to look for in 2026: For domestic use, aim for class A or B. The difference in energy consumption between class A and class D can be 30–40%.
- SEER (cooling) and SCOP (heating): Seasonal efficiency indexes. The higher the value, the more efficient the unit.
Inverter technology — why it is essential
- What it is: Inverter technology automatically adjusts the compressor speed to match the current cooling or heating demand.
- ✔ Savings: Consumes up to 40% less than a traditional On/Off unit.
- ✔ Comfort: Maintains a more stable temperature, without abrupt swings.
- ✔ Quiet: Running at variable speeds, it operates more quietly.
- Tip: In 2026, virtually all new domestic splits are Inverter. If you see a unit without this technology, skip it.
R32 refrigerant — the current standard
- What it is: R32 has replaced R410A as the standard refrigerant in most domestic air conditioning units.
- ✔ Up to 10% more efficient than R410A and requires a smaller refrigerant charge per installation.
- ✔ Complies with the revised F-Gas Regulation, which accelerates the transition to refrigerants with a lower climate impact.
- For 2026: Always choose units with R32 or R290 (propane). R410A equipment is being progressively discontinued.
6Most common mistakes when buying an air conditioner
- Buying on price alone without calculating the required capacity: A cheap unit with insufficient capacity will consume more electricity, break down sooner and never cool properly. Calculate first, then compare.
- Oversizing “just to be safe”: An oversized unit cools too quickly without properly dehumidifying the air. The result is a cold but clammy room, and short-cycling that wears out the compressor prematurely.
- Ignoring the climate zone: A unit sized for Madrid may be insufficient in Seville or oversized in Bilbao. Always apply the correction factors.
- Overlooking the energy label: The difference between class A and class D can be 150–200€ per year in electricity. Over 5 years, the higher upfront cost easily pays for itself.
- Forgetting the noise level: For bedrooms, look for units with an indoor noise level below 25 dB in silent mode. The technical data sheet always states this.
- Not asking about heat pump function: In 2026, all domestic splits should also work as heat pumps. If a unit only cools, you are missing out on the most efficient heating system available.
- Not checking whether a certified installer is required: Without an F-Gas licence, the unit may be left without warranty and the installation may breach current regulations.
7Installation and maintenance tips
Where to place the indoor unit
- Height: Between 2 and 2.5 m from the floor, on the longest wall of the room.
- Airflow direction: Do not point it directly at where people are sitting. Direct the air towards the centre of the room.
- Minimum clearances: At least 15 cm on each side and 30 cm above the unit to ensure adequate airflow.
- Avoid: Installing near heat sources (direct sunlight, lamps) or near the unit’s own thermostat sensor, as it will read incorrect temperatures.
Where to place the outdoor unit
- Ventilation: It needs clear space in front to expel heat. Never place it in an enclosed space or where airflow is restricted.
- Shade: If possible, position it in a naturally shaded spot. A unit in direct sunlight can increase energy consumption by up to 5%.
- Regulations: Check your building’s community rules before installation.
Basic maintenance to make it last longer
- ✓️ Clean the filters every 15–30 days during the season. This is the most important and most overlooked maintenance task.
- ✓️ Annual service by a certified technician before each season begins.
- ✓️ Optimal temperature between 23 and 26 °C. Every degree below 23 °C adds 7–8% to electricity consumption.
- ✓️ Check the refrigerant charge every 2–3 years if you notice the unit is not cooling as well as it used to.
- ✓️ Wipe the louvres and outer casing with a damp cloth. Dust build-up reduces efficiency.
8Frequently asked questions about choosing the right air conditioner
QHow many frigories do I need for 20 m²?▼
For a room of 20 m² with a standard ceiling height of 2.5 m, you need approximately 2,000 – 2,500 frigories (2.0 – 2.9 kW). If the room has high solar exposure or you are in a warm climate zone (Andalusia, Canary Islands), go up to 2,500 – 3,000 frigories.
QHow many frigories for a 30 m² living room?▼
For a 30 m² living room, the indicative capacity is 3,000 frigories (3.5 kW). With large windows, in a top-floor flat or in climate zone B (Seville, Córdoba), go up to 3,500 – 4,000 frigories to ensure adequate performance.
QIs it better to oversize or undersize the unit?▼
Undersizing means the unit runs at full capacity without reaching the target temperature, increasing consumption and wear. Oversizing means the unit cools too quickly without properly dehumidifying, resulting in a cold but humid feeling and short-cycling that reduces compressor life. Neither option is correct.
QWhat is the difference between frigories and kW?▼
Frigories and kW measure the same thing: cooling capacity. The conversion is direct: 1 kW = 860 frigories. A 3.5 kW unit equals 3,010 frigories. Modern catalogues show frigories, kW and BTU — three ways of expressing the same value.
QWhat is better: 1×1 split or multi-split?▼
For a single room or living area, the 1×1 split is more efficient and cost-effective. For 2 or more independent rooms, the multi-split is the better option: one outdoor unit with individual control in each room, avoiding multiple machines on the facade.
QCan an air conditioner also heat in winter?▼
Yes, as long as the unit includes a heat pump (Heat mode). In 2026, virtually all new domestic splits include this function. For every kW of electricity consumed, it can generate 3–4 kW of heat — a saving of up to 60–70% compared to direct electric heating.
QDo I need an F-Gas certified installer?▼
Yes, the installation of any unit with a refrigerant circuit requires an F-Gas certified installer. Without this, the installation may be left without warranty and may breach current regulations. For units over 4,500 frigories, registration with the regional Industry authority is also mandatory.
QHow much electricity does an air conditioner use per month?▼
A 3,500 frigory (class A, Inverter) split running 8 hours a day consumes between 80 and 120 kWh per month, equivalent to roughly 20–35€ at current electricity prices in Spain. Keeping the temperature between 23 and 26 °C and not opening windows while the unit is running are the most effective ways to reduce consumption.
Choosing the right air conditioner for your square metres is the most important decision before you buy. Once you have calculated the required frigories using the correction factors in this guide, always choose a unit with Inverter technology, R32 refrigerant and an A or B energy label to ensure maximum performance and minimum running costs.
Remember: the purchase price is only part of the total cost. A well-chosen air conditioner can save you 150–200€ a year in electricity over a lifespan of 10–15 years. Always consult a certified installer for a definitive calculation and an installation that guarantees the optimum performance of your unit.
