What temperature to set your air conditioner to, and what each degree costs

Updated August 25, 2026 · Claude AC · 2 sources cited

Contents (5)

The arithmetic of one degree
Where Europe’s 27 °C figure came from
Comfort is not only temperature
A setpoint strategy that works
Frequently asked questions

The setpoint is the only free lever an air conditioner owner has. Efficiency is fixed the day the machine is bought, sizing is fixed the day it is installed, the tariff is fixed by the market — but the number on the remote is chosen anew every afternoon, and it moves the bill more than any other single decision. The physics is unforgiving in a useful way: cooling energy scales with the temperature difference the machine has to maintain, so on a 34 °C afternoon, asking for 21 °C is roughly twice the work of asking for 26 °C.

The arithmetic of one degree

The International Energy Agency and the European Commission put a number on it during the 2022 energy crisis: setting an air conditioner one degree warmer cuts its electricity use by close to 10 %. The figure is a European average across building types, and the exact percentage in your flat depends on outdoor temperature, insulation and run hours — but the order of magnitude holds everywhere, and it compounds.

Read the table as an indicative index, not a promise: it shows how cooling demand moves with the setpoint for a typical European flat on a hot day, all else equal.

Setpoint	Indicative cooling energy vs 26 °C	Verdict
21 °C	roughly +50 % to +60 %	Uncomfortably cold for most people, and the most expensive setting on the dial
23 °C	roughly +30 %	Common default; comfortable but rarely necessary in a dehumidified room
25 °C	roughly +10 %	The pragmatic setting for heat sensitivity, small children or elderly occupants
26 °C	reference	The usual sweet spot for a European home with fans and shading
27 °C	roughly −10 %	Comfortable with air movement and modest humidity; the public-building standard
28 °C	roughly −20 %	Fine at night in a dry climate, marginal in Mediterranean humidity

Two consequences follow. First, the cheapest degree you can buy is the one you never ask the machine for: closing shutters before the sun lands on the glass is worth 2 to 3 °C for nothing. Second, the machine’s own efficiency multiplies this — a high-SEER inverter running at 26 °C and a mediocre unit running at 26 °C spend very different amounts for the same comfort, which is what the classes on the EU energy label actually mean.

Where Europe’s 27 °C figure came from

The number circulating on European social media every heatwave has a real origin and a widely misreported scope. In August 2022, Spain’s Royal Decree-Law 14/2022 required public buildings and commercial premises — offices, shops, bars, cinemas, stations, airports — not to cool below 27 °C. Italy had done something comparable a few months earlier: under « Operazione Termostato », summer cooling in public buildings had to average no less than 27 °C, with a 2 °C tolerance and hospitals excluded, from May 2022 to March 2023.

Both measures were emergency energy-saving rules tied to the gas crisis, both were time-limited, and neither ever applied to private homes. The Spanish limits ran their course and were not renewed; the recurring claims that Spain « bans » households from cooling below 27 °C have been repeatedly fact-checked as false. What survives is the figure itself as guidance — a reasonable public-building target that turns out to be a reasonable domestic one too, provided the rest of the comfort equation is handled.

Comfort is not only temperature

The reason 27 °C feels fine in one room and oppressive in another is that human comfort depends on four variables, and the thermostat controls one of them.

Humidity

At 60 % relative humidity, sweat evaporates poorly and 27 °C feels heavy; at 45 %, the same air feels pleasant. An air conditioner dehumidifies as a side effect of cooling, which is why a room can feel better at 26 °C after an hour of running than it did at 24 °C in the first ten minutes. In humid Mediterranean and Atlantic summers, targeting humidity rather than temperature is often the smarter strategy.

Air movement

A ceiling or pedestal fan raises the acceptable temperature by roughly 2 to 3 °C for a few watts, because moving air carries heat off the skin. A fan plus 27 °C consumes dramatically less than still air at 24 °C and is frequently more comfortable. This is the single best value pairing in summer cooling.

Radiant temperature

A west-facing wall that absorbed sun all afternoon radiates heat into the room long after sunset; the thermostat reads air, not walls, which is why a room can measure 25 °C and feel like 28 °C. External shading — shutters, awnings, blinds outside the glass — attacks the problem at source; internal curtains barely do.

Adaptation

Comfort expectations shift with what your body is used to. Somebody spending a Seville August outdoors is comfortable at 27 °C indoors; somebody stepping out of a 21 °C office is not. That adaptive effect is well established in thermal comfort research and is why fixed « ideal temperature » claims travel badly across Europe.

A setpoint strategy that works

Hold one steady setting rather than chasing. An inverter compressor is most efficient modulating gently around a stable target; crash-cooling an overheated room from 30 °C costs more than never letting it get there.
Do not switch it off when you leave for a couple of hours — raise the setpoint by 3 to 4 °C instead. Reheating the building fabric costs more than holding it.
Night: 25 to 27 °C with air movement, on the sleep or night programme, which caps fan and compressor speed and drifts the setpoint up over the night. Sleep quality degrades in heat, but it degrades in cold draughts too.
Ignore the « never more than 8 °C below outdoors » folklore. There is no physiological threshold at eight degrees; the real advice is to avoid direct cold draughts on the body and abrupt changes, which is a placement and airflow question.
Use dry mode with judgement. It targets humidity at reduced airflow and is excellent in muggy weather — but it is not a low-cost cooling mode, and on some units it runs longer for the same result.
Check the sizing before blaming the setpoint. A room that never reaches 26 °C on a hot afternoon is usually undersized or under-shaded, not badly set — our kW sizing guide has the method.

Households with heat-vulnerable occupants should reverse the priority order without guilt: during a heatwave, a cool room is a health intervention, and the extra kilowatt-hours are cheap against the alternative. European heatwave mortality is concentrated in exactly the households that hesitate over the bill. What that bill really looks like, tariff by tariff, is worked out in our guide to running costs across Europe.

Frequently asked questions

What is the ideal air conditioner temperature in summer?

For most European homes, 25 to 27 °C combined with a fan and closed external shading. Below 24 °C the cost climbs steeply for comfort gains that air movement and lower humidity would have delivered for a fraction of the energy.

Is it illegal to set air conditioning below 27 °C in Spain or Italy?

Not in a private home, and not any more in public buildings either. Both countries applied 27 °C limits to public and commercial premises as temporary energy-crisis measures in 2022; those measures were time-limited and have lapsed. Viral claims that households face a legal limit are false.

Does turning the air conditioner off when I go out save money?

For a short absence, no — raising the setpoint a few degrees beats switching off, because the walls and furniture reheat and must be cooled again. For a full day away, switching off wins, ideally with a scheduled restart shortly before you return.

Does setting a lower temperature cool the room faster?

No. A thermostat is a target, not a throttle: an inverter reaches full output as soon as the gap is large, and setting 18 °C simply means it never stops once it gets there. Set the temperature you want and let it modulate.

Why does my room feel hot even though the thermostat reads 25 °C?

Usually humidity or radiant heat from sun-loaded walls and glass, sometimes a sensor reading warm air near the unit rather than room air. Check humidity, shade the glass from outside, and if the unit runs constantly without reaching its target, check filters and coils — the maintenance basics are in our European maintenance guide.