What temperature should you set your air conditioning to in summer?

Cool enough to feel well, not so cold that you pay for it.

The answer in 2 lines. England has no legal rule on what temperature to set home air conditioning, and GOV.UK and the NHS give no official target. The useful rule is simple: choose a comfortable setting a few degrees below the outdoor temperature, not the lowest the remote allows. Keep doors, windows and curtains closed in the cooled room, and switch the unit off when nobody is there. Every degree lower makes the unit work harder and puts up your bill. For babies, older people and anyone unwell, avoid cold air blowing straight at them. If someone shows signs of heatstroke, call 999.

The first 3 steps

Pick a moderate setting, a few degrees below the temperature outside, then adjust one degree at a time until you are comfortable.
Close windows, doors and curtains in the room you are cooling, especially on the side that gets the sun.
Use the timer or schedule instead of leaving the unit on in an empty room.

The right setting for the moment

Hot afternoon: a comfortable setting a few degrees below the outdoor temperature. A very low setting does not cool the room faster, it just makes the unit run for longer.
Night: use the sleep or night mode if your unit has one, or raise the setting by a degree or two. If possible, sleep in the coolest room in the house, as GOV.UK advises.
Out for a few hours: switch off, or set a higher temperature. Cooling an empty room is wasted money.
Muggy, humid air: the "dry" or dehumidify mode is often enough to feel better.
Cooler evening: switch off and open the windows when the air outside feels cooler than inside, as long as it is safe to do so.

Fan or air conditioning?

A fan cools you, not the room. UKHSA says to use one only when the air temperature is below 35°C, and not to aim it straight at your body. The Energy Saving Trust says a fan is the cheapest way to cool down.
A portable air conditioner cools a room quickly but uses far more electricity than a fan. The Energy Saving Trust advises using a fan first if you only need to cool yourself.
An air-to-air heat pump that already heats your home can often cool it too: ask the installer about the cooling setting.

Babies, older people and anyone unwell

UKHSA says people aged 65 and over, babies and young children, pregnant women, people who live alone and people with some long-term conditions are more at risk in the heat.
Do not let cold air blow straight at a cot, bed or armchair, and avoid big temperature changes between rooms.
A room cooled for a few hours a day already helps a lot during a heatwave.
Keep everyone drinking regularly, even if they are not thirsty, and check on older neighbours.

Stop: danger

Signs of heatstroke (very high temperature, hot skin that is not sweating, fast breathing, confusion, fits, loss of consciousness): call 999. While you wait, move the person somewhere cool, and cool them with a wet sheet, cold water or a fan.
Heat exhaustion (heavy sweating, dizziness, headache, cramps, intense thirst): move the person somewhere cool, give them water and cool their skin. If they still feel unwell after 30 minutes, call 999. If you are struggling to treat the symptoms or need advice, call NHS 111.

What not to do

Setting the remote to the lowest temperature to cool the room faster: it won't work, and it costs more.
Pointing the cold airflow at a bed or sofa.
Leaving a window open while the air conditioning is running.
Opening windows in the middle of a hot afternoon when it is hotter outside than inside.

In England

Heat-health alerts: UKHSA and the Met Office issue yellow, amber or red alerts for England. The core season runs from 1 June to 30 September. See the Met Office heat-health alert service, where the "Sign up for alerts" section explains how to get them by email.
Get your home ready: the GOV.UK Beat the heat: keep cool at home checklist helps you work out whether your home is likely to overheat. Go through it before summer: check that fans, fridges and any ventilation system work, and plan how you will shade the windows.
The cost: from 1 October to 31 December 2026, the Ofgem price cap puts the average electricity unit rate at 26.32p per kWh by Direct Debit. Every hour the unit runs for nothing shows up on the bill.

Wales, Scotland and Northern Ireland have their own public health bodies, but the advice on keeping cool is the same.

Good to know

No air conditioning? See How to keep your home cool without air conditioning.
Clean filters cool better and use less power: see How to clean your air conditioning filters safely.

During a July heatwave in Birmingham, Lucy sets her air conditioning as low as it will go and wakes up with a dry throat. She switches to a more moderate setting during the day and sleep mode at night, and draws the curtains on the sunny side in the morning. She sleeps better, and her electricity use for August drops noticeably.

A made-up story, for illustration.

Bobby

Sources, verification, confidence

Verified on 6 November 2026, for England. Confidence: high for the health advice, the groups most at risk, the 35°C fan limit and the heat-health alert service; high for the electricity unit rate (Ofgem, October to December 2026); medium for the setting advice, because no official UK body publishes a recommended temperature for home air conditioning. How much you save per degree depends on the unit and the home.