How to stay cool without air conditioning

The key insight: it is much easier to stop heat getting in than to remove it once it's inside. Most of these strategies work by intercepting heat at the building envelope — before it ever warms your rooms.

Block the heat

Glass is a terrible insulator. On a sunny day, a south- or west-facing window can let in more heat than a radiator puts out. Your first move is to intercept the sun before it heats the room.

• Close blinds and curtains on sun-facing windows during the day. Do this before the sun hits the glass, not after the room has already warmed up. Thick or blackout curtains are most effective.
• External shading beats internal blinds. Awnings, external shutters, pergolas and overhanging roofs stop the sun's heat before it reaches the glass. Even a purpose-fitted roller blind on the outside of a window is more effective than one inside.
• Light colours reflect. Light-coloured curtains, blinds and — where you have a choice — roof and wall colours reflect more heat than dark ones. This matters most on roofs and south/west-facing walls.
• Seal gaps. Hot outdoor air sneaking in through draughts raises indoor temperature quickly. The same draught-proofing that keeps warmth in during winter keeps heat out in summer.

Ventilate smartly

Ventilation is your best free cooling tool — but timing matters. Letting in hot midday air makes rooms hotter, not cooler.

• Open up at night and during cooler morning hours. Many climates are 10°C or more cooler after midnight than at midday. Leave windows open overnight (with security in mind) to flush out the heat stored in walls and floors.
• Create cross-ventilation. Open windows or vents on opposite sides of the house to create a through-draught. Even a gentle breeze through the building removes heat far more effectively than still air.
• Open high and low. Hot air rises. Opening a high window (or a rooflight, if you have one) and a low window on the opposite side creates a stack effect that pulls warm air up and out even on calm days.
• Close up before it gets hot. Once indoor air is cooler than outdoor air — usually mid-morning — close windows and external doors to trap that cool air inside for as long as possible.

Use fans well

Fans are useful, but they are frequently misunderstood.

• Fans cool people, not rooms. A fan moving air across your skin increases evaporative cooling and makes you feel several degrees cooler — but it adds a little heat to the room (from the motor). Turn fans off in empty rooms.
• Box fan in a window at night. Position a box fan facing outward in a window on the warmer side of the house (often the side where warm air has accumulated). Open windows on the cooler side. This pulls cooler night air through the house very effectively.
• Ceiling fan direction. In summer, ceiling fans should spin counter-clockwise when viewed from below (this is the "forward" or summer setting on most fans). This pushes air straight down, creating a wind-chill effect on people below. The winter setting (clockwise, low speed) draws cool air up and redistributes warm air sitting near the ceiling.
• Use fans with damp air. Placing a shallow bowl of ice or a damp towel in front of a fan cools the air it blows slightly. This works best in low-humidity climates.

Cool your body directly

Your body's cooling system is sweat evaporation. These techniques support it.

• Stay hydrated. Your body sweats to cool itself; if you are dehydrated, sweating becomes less effective. Drink water regularly, more than usual in hot weather — don't wait until you feel thirsty.
• Damp cloth on pulse points. A cool, damp cloth applied to wrists, the back of the neck or the insides of elbows cools you quickly because major blood vessels sit close to the skin at those points.
• Cool shower or foot soak. A lukewarm (not ice-cold) shower or soaking your feet in cool water is remarkably effective and the effect lasts for a while afterwards.
• Lighter bedding. Switch to a single cotton sheet instead of a duvet. Linen or cotton breathe much better than synthetic fabrics. Keeping your bedroom curtains closed all day makes a big difference to how cool it is by bedtime.
• Loose, light-coloured clothing. Loose-weave, light-coloured fabric in natural fibres (cotton, linen) allows more air circulation and reflects heat better than dark or synthetic options.

Reduce indoor heat sources

Everything that uses electricity or burns gas in your home produces heat as a byproduct. On a hot day, these sources add up.

• Avoid using the oven. A conventional oven running for an hour adds significant heat to your kitchen. Cook outside on a barbecue or portable hob, use a microwave, air fryer or slow cooker, or eat cold meals during a heatwave.
• Switch to LED lighting. Incandescent and halogen bulbs convert most of their energy to heat rather than light. LEDs produce very little waste heat — another reason to make the switch.
• Switch off electronics when not in use. TVs, games consoles, desktop computers and routers all generate heat while running. Turn them off rather than leaving them on standby during the hottest hours.
• Use the dishwasher and washing machine at night. These appliances generate heat and humidity when running. Running them overnight means any warmth they produce dissipates while you are ventilating.

Longer-term improvements

If you own your home and want to invest in permanent comfort without AC, these have the best returns:

• Insulation keeps heat out as well as in. A well-insulated loft/attic and cavity walls dramatically slow the rate at which outdoor heat penetrates your home — the same insulation that cuts your heating bill also cuts summer heat gain. See our home insulation guide.
• Reflective window film. Thin solar control film applied to existing windows reflects a significant proportion of solar heat gain without blocking light as much as blinds do.
• External shutters or awnings. These are common in southern Europe for good reason. A fixed or adjustable awning on a south- or west-facing window can cut solar heat gain through that window by 65–75%.
• Shade trees and climbing plants. A deciduous tree on the sunny side of the house provides dense summer shade and then loses its leaves in winter, allowing winter sun through. Climbing plants on a trellis have a similar effect and also keep the wall behind them cooler.
• Thermal mass. Tiled or stone floors absorb heat during the day and release it slowly at night. If you are remodelling, stone and tile are cooler underfoot and better at regulating temperature than carpet.

Your stay-cool checklist

• Close blinds or curtains on south- and west-facing windows before the sun hits them.
• Keep the house closed and shaded during peak heat hours (late morning to early evening).
• Open windows on opposite sides of the house once outdoor air cools — especially at night.
• Use fans only when people are in the room; try a box fan in a window at night.
• Drink water regularly throughout the day, more than you think you need.
• Apply a cool damp cloth to wrists and neck for quick relief.
• Switch to lighter bedding (cotton sheet, not a duvet) and keep the bedroom dark all day.
• Avoid using the oven; use a microwave, barbecue or eat cold meals instead.
• Turn off lights and electronics that are not in use.
• Check on neighbours and relatives, especially older adults, during hot spells.