Cross ventilation: how to keep your home cool during a heatwave without air conditioning

Heatwaves arriving earlier, and not every home has air conditioning

As temperatures climb to extreme levels as early as May, some households still have no air conditioning. Fortunately, there is plenty to learn from earlier generations, who knew how to stay cool in harsh conditions without any air-con.

In some areas, installing an air conditioning system is almost a given, but that is far from universal. In the northern half of France, people are more inclined to spend money on heating for the long winter months. When a heatwave hits, however, keeping the indoors comfortable can be a real challenge.

“How did our grandparents manage without air conditioning?” Many people in France have likely asked themselves that in recent days, as new temperature records were set across the country. Although heatwaves are more frequent now, older generations still have practical advice worth following.

The power of cross ventilation

Among the tips passed down over time, cross ventilation is one of the simplest and most effective to put into practice. The idea is to manage how you air your home so a natural draught flows through the rooms, replacing stagnant hot air with a cooler breeze. Traditional builders often designed houses with this in mind, favouring openings placed strategically on opposite or perpendicular walls to encourage airflow.

How to set up cross ventilation day-to-day

In practical terms, the approach depends on three key principles:

• Open windows wide in the evening, especially those facing each other or located on opposite sides, so the cooler night air can pass through and flush out the heat stored during the day.
• From early morning, shut shutters and close windows on the sun-facing side to stop heat from pouring indoors.
• Keep open only a few openings on the shaded side, maintaining gentle airflow without drawing in hot air.

In Mediterranean villages, you can still see these morning habits: curtains drawn, louvred shutters left slightly ajar, and homes kept in half-light until evening. This long-standing routine remains highly relevant as heatwaves become more frequent.

Why does it still work?

The effectiveness of cross ventilation comes from using naturally occurring differences in temperature and air pressure between outdoors and indoors. Night-time coolness lowers the temperature of walls and floors, which then retain that coolness and release it during the day, slowing the rise in indoor temperature. Meanwhile, warm air is kept outside by closing openings on the side exposed to the sun.

At a time when air conditioning is being questioned by public authorities (for economic, environmental or health reasons), these techniques can stand out as worthwhile alternatives. That said, some heatwaves reach such extremes that it becomes hard to cool homes down at night. In the south of France, temperatures did not drop below 30°C in the middle of the night. Without air conditioning, it is difficult not to suffer in the heat.