Short answer: Keep sun off windows during the day with curtains, blinds or external shading, ventilate at night when the outside air is cooler, reduce heat from appliances and lighting, and use fans for air movement. If rooms regularly stay above about 26 °C at night, a fixed air conditioning system is the most reliable fix.
Block the sun
Most daytime heat comes through glass. Close curtains and blinds on sunny sides, ideally light-coloured; external shading works best.
Purge at night
Open windows when it is cooler outside than inside, usually late evening to early morning, and close them again by mid-morning.
Reduce internal heat
Switch off unused electronics, use the oven less, and swap old bulbs for LEDs.
When to consider air conditioning
If bedrooms stay hot overnight, if someone vulnerable lives in the home, or if a room is unusable for weeks each summer.
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More guides
- How much does air conditioning cost to install in the UK?
- How much does air conditioning cost to run?
- What size air conditioner do I need?
- Fixed split or portable air conditioning?
- Do you need planning permission for air conditioning?
- The £2,500 grant for air-to-air heat pumps explained
- F-gas rules: what homeowners need to know
- R32, R410A and R22: refrigerants explained
- Is air conditioning the same as a heat pump?
- What happens on air conditioning installation day
- Air conditioning noise and your neighbours
- Looking after your air conditioning: an owner's checklist
- Can you fit air conditioning in a listed building?
- Air conditioning in a flat: leases, freeholders and planning
- Multi-split or separate single systems?
Reviewed October 2026. Rules and prices change; check the date and ask us if anything is unclear.