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What temperature should the air conditioning be set to?
The argument of every Spanish living room, settled with thermodynamics and real bills: the right number, why 18 °C is ruinously expensive, and how to sleep cool without waking up with a dry throat.
Quick summary
The rational setpoint in Valencia: 24–26 °C by day (start at 25), 26–27 °C at night with sleep mode. Every degree lower adds 7–8% consumption: from 25 to 20 °C the bill grows ~40%. Comfort is not only temperature: with dry, moving air, 25 °C feels like 23.
The number — and the science behind it
A resting body in light clothing is comfortable between 23 and 26 °C with controlled humidity. Below 22 °C in summer, you enter thermal contrast with the street (32–36 °C in Valencia): the shock at the door, the dry throat, the classic July cold. Spain's official guidance (RITE, public buildings) does not go below 27 °C in summer for efficiency; our honest domestic recommendation is 25 °C — the point where real comfort and the bill make peace.
The fact that changes the argument: air conditioning dehumidifies, and humidity weighs as much as temperature in how a room feels. A living room at 25 °C and 45% humidity feels better than one at 23 °C and 70%. That is why a correctly sized unit (one that genuinely dries) allows higher setpoints at the same comfort — and why the oversized unit that "cools super fast" leaves the air sticky.
What each degree costs
| Setpoint | Relative consumption | Typical monthly bill (living room, 8 h/day) |
|---|---|---|
| 27 °C | base −15% | €17–34 |
| 25 °C (recommended) | base | €20–40 |
| 23 °C | +15% | €23–46 |
| 21 °C | +30% | €26–52 |
| 18 °C ("fridge mode") | +55% and the unit barely stops | €31–62 and accelerated wear |
18 °C also has a dirty secret: in a real heat wave many units never even reach it, so the compressor runs at 100% perpetually — the recipe for premature wear and the August breakdown.
Night: sleeping cool without catching cold
- Sleep/night mode: raises the setpoint 0.5–1 °C per hour while you sleep. Your body cools down at night — you don't need 11 pm's 24 °C at 4 am.
- 26–27 °C with moving air (oscillating louvres or a ceiling fan on minimum) sleeps better than 23 °C with a fixed stream.
- Louvres upward, never at the bed: cold air falls on its own.
- A timer if your home holds the cool: switch-off after 3–4 h in well-insulated bedrooms — silence rests too.
FAQ
What temperature should the air conditioning be set to? — FAQ
Is sleeping with the AC on bad for you?
With the right setpoint (26–27 °C, sleep mode, louvres up) and a clean unit, no: it is healthier than sleeping in sweat. The problems (throat, stiff neck) come from direct streams, excess cold and dirty coils spreading what they accumulate — all avoidable.
Why do I catch colds from air conditioning?
Three culprits: a setpoint too low (thermal contrast), a direct stream on the body, and an uncleaned unit distributing what it hoards. The fix: 25 °C, louvres up, and the annual clean with disinfection.
Does "eco" mode actually do anything?
It does: it caps power and softens the setpoint, cutting 10–20% consumption in exchange for slightly slower cooling. For long sessions (whole afternoons, nights) it is exactly the right mode.
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