Choosing an air conditioner: type, size and efficiency

Split or portable: which type should you buy?

Buy a split unit if you can install one; buy a portable only if drilling through the wall is not an option or you need cooling for a few days a year.

A split unit keeps the compressor and the hot side outdoors, linked to the indoor unit by refrigerant pipes. A portable (single-duct) unit sits entirely in the room and blows warm air out through a hose; that air is replaced by warm outside air drawn in through doors, gaps and the window slot. EU rules even require single-duct units to be sold as “local air conditioners”.

An A+ portable and an A+ split unit are not equally efficient: the two types use different measurements and different class thresholds. Compare yearly kWh, not letters, across types.

How much cooling power does your room need?

Size the unit to the room’s cooling load, which depends more on sun, glazing, insulation and ceiling height than on floor area alone.

The label of a split unit states the design load for cooling in kW: the output the unit delivers at the reference outdoor temperature of 35 °C. A sunny attic room needs far more than a north-facing room of the same size in a well-insulated building. A heavily oversized unit cycles more and dehumidifies less, even with an inverter; an undersized one runs flat out on hot days. Beyond a single room, ask the installer for a heat-load calculation.

The table groups models by type and cooling power, the same bands used in our air conditioner overview. Compare running costs only within one band: a larger unit naturally uses more over a season.

What do SEER, SCOP and EER on the label tell you?

They are efficiency ratios, cooling or heating delivered per unit of electricity, so higher is always better.

• SEER (seasonal energy efficiency ratio) covers a whole cooling season, including the many hours a split unit runs at part load. The label turns it into kWh per year for a reference season of 350 full-load-equivalent hours.
• SCOP (seasonal coefficient of performance) does the same for heating. A SCOP of 4 means four units of heat for every unit of electricity across the heating season.
• EER is measured at a single steady test point. Portable units are rated this way because, when the rules were written, none had variable-speed compressors.

The labels are set by Delegated Regulation (EU) No 626/2011, and the ecodesign minimums by Regulation (EU) No 206/2012. Both are under review, but at the time of writing air conditioners still carry the A+++ to D scale. The label explainer for air conditioners walks through each field, and the best cooling efficiency list ranks split units by SEER.

Is it worth heating with an air conditioner?

A reversible split unit is an air-to-air heat pump, and in mild and average climates it can heat a room with a fraction of the electricity a direct electric heater needs.

The label shows SCOP for up to three European heating seasons on a small map: average (designed for −10 °C outside), warmer (+2 °C) and colder (−22 °C). Only the average season is mandatory; the others may be marked “X”. Most of central Europe sits in the average zone. Our yearly costs add heating in the average climate wherever the label declares it, and each model page has a climate table if you live somewhere colder or warmer.

If you plan to heat with it, rank by SCOP rather than SEER: our best heating efficiency list does exactly that.

How loud will it be indoors and outside?

The label states sound power in dB(A) for the indoor unit and, for split units, the outdoor unit; lower is better, and 10 dB more sounds roughly twice as loud.

EU ecodesign rules cap split units up to 6 kW at 60 dB(A) indoors and 65 dB(A) outdoors, and units between 6 and 12 kW at 65 and 70 dB(A). Portable units may reach 65 dB(A) in the room. These values are measured at full output; at night a split unit usually runs well below that, while a portable unit has its compressor next to your bed. For bedrooms, start from the quietest air conditioners, and place the outdoor unit away from neighbours’ windows: many countries limit noise at the neighbour’s property, especially at night.

Does the refrigerant matter?

Yes, because the EU F-gas Regulation (EU) 2024/573 is phasing out climate-damaging refrigerants in new air conditioners step by step.

• Portable (plug-in) units with HFCs of GWP 150 or more have been banned from sale since 1 January 2020; they now use alternatives such as propane (R290).
• Single split systems with under 3 kg of refrigerant and a GWP of 750 or more have been banned since 1 January 2025, which ended new units with the older R410A.
• From 1 January 2029, new split air-to-air units up to 12 kW may not use F-gases with a GWP of 150 or more, which includes R32 (GWP 675). From 1 January 2035 they may not use F-gases at all. Both bans allow exceptions where safety rules require it.

These bans apply to new equipment placed on the market; a unit that is already installed can keep running and be serviced. Each model page lists the refrigerant and its GWP.

Who may install it, and how long will it last?

A split unit charged with fluorinated refrigerant may only be sold to you with evidence that a certified company will install it.

In a rented flat or a building with shared ownership, you will normally need consent before drilling through an outside wall. Unlike fridges or washing machines, air conditioners have no EU ecodesign rule on spare parts or repair information, and they are not covered by the EU right-to-repair directive. Ask the installer which parts and service they offer and for how long, and keep the filters clean: clogged filters cost efficiency.

What will it cost to run, and when does replacing an old unit pay off?

The running cost is the label’s yearly kWh multiplied by your electricity price, so the same unit costs very different amounts across Europe.

To judge a replacement, take the old unit’s yearly kWh from its label or fiche, subtract the new unit’s figure for the same cooling power and climate, and multiply by your price from the electricity prices by country. Divide the cost of the new unit and its installation by that yearly saving, and compare the years with the life you expect from it. The total cost of ownership calculator does the arithmetic. Replacing a portable unit with a split unit usually changes more than replacing one split unit with a newer one.

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