Long before air conditioning existed, entire civilisations learned to live, and sleep, through 45°C in the shade. From Cairo to Marrakech, Seville to Baghdad, their techniques have been handed down for generations because they work, cost nothing and use not a single watt. British homes, built to trap heat, respond remarkably well to them. Here are five to put into practice today, with the physics behind each one.

1. A fortress by day, wide open by night

The golden rule across the Mediterranean: during the day, the house is sealed: blinds down, curtains drawn, windows shut on the sunny side. It feels counterintuitive, but a sunlit pane of glass behaves like a radiator. From sunset to dawn, do the opposite: everything open, to flush out the heat stored in the walls. Applied consistently, this single habit can keep the inside several degrees below the outside.

2. The chimney effect that empties the heat out

In the traditional buildings of the Gulf, wind towers draw cool air in low and push hot air out high. In a house or flat, the principle works at night: open one window low on the cool side (the garden, the north face) and one high on the opposite side, a landing window or a skylight is ideal. Hot air, being lighter, rises and escapes; cooler air is pulled in below. The through-draught empties the house of heat far faster than two windows on the same side ever will.

3. The wet sheet at the window: ancient Egypt's fridge

A technique recorded as far back as ancient Egypt: a wrung-out wet sheet hung in front of an open window at night. Air passing through it makes the water evaporate, and evaporation absorbs heat: the air enters the room a few degrees cooler. It works best when the air is dry, and the sheet needs re-wetting once it dries out. Total cost: nothing.

4. Switch off everything that heats the room for no reason

Every appliance left on is a small radiator: the TV on standby, the PC left running, the oven at lunchtime, halogen bulbs. In extreme climates, cooking during the hot hours is simply out of the question. Shift the oven, dishwasher and tumble dryer to late evening: the house gains twice: less heat produced, and produced at a time when it can escape through open windows.

5. Make your fan a smarter ally

A fan doesn't cool the air, it cools you, which is a different strategy altogether. Point it at your body, not the ceiling; at night, sit it in the window facing outwards to expel warm air and speed up the exchange; and for a targeted blast of cool, a frozen bottle in front of the airflow chills the stream heading your way. Total running cost: pennies a night at the current price cap rate, against several pounds a day for a portable air conditioner.

Why they work best together

The secret of these techniques is that they stack. Closed curtains stop the sun turning your windows into radiators; night-time cross-ventilation flushes out the heat the walls have stored anyway; the wet sheet cools the air coming in; the absence of indoor heat sources stops you undoing by day what the night achieved; and the fan makes the worst hours bearable. Applied together and consistently, they are easily worth 3–5 degrees of felt temperature, the equivalent of what many people ask of an air conditioner, without the noise, the installation or the line on the bill. For a sense of scale: an oven run at midday dumps 1–2 kWh of pure heat into your kitchen, which no trick can compensate for.

Worth remembering: seal by day, cross-ventilate by night, harness evaporation, produce no heat indoors, and aim the fan at yourself. Five zero-cost habits that together are worth several degrees of felt temperature, and no nasty surprise on the bill at the end of summer.