In a nutshell 💡
- The first step isn’t to cool down—it’s to keep the heat out. Keep shutters closed during the day and windows open at night.
- A fan doesn’t cool the air—it speeds up the evaporation of your sweat. On dry, still skin, its effect is minimal.
- Damp cloth in a draft works, and for a specific reason: the evaporating water draws heat away.
- Cooling a person costs infinitely less than cooling a volume of air. This is the strategy that almost no one uses.
- In some cases, air conditioning remains the right solution, and it’s better to acknowledge that than to deny it.
How many degrees does your home heat up between 8 a.m. and 6 p.m. on a heatwave day? For many people, the answer far exceeds what any fan can make up for by evening.
That’s the whole problem with solutions that don’t involve air conditioning: they’re often used too late, on a home already loaded with heat, when they would have been incredibly effective as a preventive measure. And an entire aspect of the issue is almost always overlooked.
Here’s what actually works, in the order that matters, along with what each method can and cannot do.
See also: Heat, heat waves, heat exhaustion: the right habits to adopt this summer
Preventing heat from entering: the only truly decisive step
A home heats up due to solar radiation passing through the windows. Once this energy enters, it is absorbed by the walls, floors, and furniture, which then release it for hours. No amount of ventilation can reverse this process afterward.
The top priority, therefore, is to block the sun before it passes through the window.
- Exterior shutters are the most effective solution because they block the radiation outside the window
- Exterior awnings and sunshades do the same job on windows that don’t have shutters
- Interior curtains help, but to a lesser extent: the heat has already entered, so they mainly limit direct radiation on surfaces
- Heat-blocking window films permanently reduce solar heat gain, even when you’re away
The key habit to adopt is: keep windows closed during the day, open them at night. As soon as the outside air becomes cooler than the inside air—usually late in the evening—open the windows wide to let the stored heat escape. Opening windows in the middle of the day simply lets in the hot air you were trying to avoid.
Create a draft, not just an open window
A single open window provides almost no ventilation. You need two openings on opposite sides to create cross-ventilation. If the layout allows, one opening at the bottom and one at the top create a chimney effect: warm air rises and escapes, while cooler air enters from below.
Three tips for truly effective nighttime ventilation:
- Wait until the outside air is cooler than the inside air—often later than you’d think in the city, where the asphalt radiates heat for much of the night
- Open windows wide rather than leaving them ajar: airflow matters more than duration
- Close the windows before the sun hits the facade, without waiting for the outside temperature to rise again
The fan: very useful, but not for the reason you might think
A fan doesn’t produce any cool air. It moves air, and this moving air speeds up the evaporation of your sweat. It’s your body that cools down, not the room.
This distinction has three practical implications. A fan running in an empty room serves no purpose and even slightly warms the air due to the motor. Its effectiveness depends on how much you sweat—and thus on your hydration. And when the ambient air exceeds body temperature, it can become counterproductive by blowing air that’s warmer than your skin.
Two uses make the most of it:
- Set it to exhaust mode, facing an open window, to drive hot air outside overnight
- Combine it with water: damp skin, a wet cloth, or a mist. That’s when the benefit really becomes noticeable
The damp cloth: a technique based on physics
Hanging a wet sheet in front of an open window or a fan works. The water in the fabric evaporates, and this change of state draws heat from the surrounding air. This is the principle of so-called evaporative cooling, which has been used since ancient times.
There are two limitations, however. The effect increases the humidity in the room, which quickly becomes unpleasant and counterproductive in an already damp home. And moving air is necessary; otherwise, evaporation stops on its own once the local air is saturated.
Heat sources we create ourselves
A home also heats up from the inside, and this factor is largely underestimated. Every electrical appliance in use converts part of its energy into heat.
- The oven and stovetop are by far the biggest culprits: cooking at noon can raise the temperature in a kitchen by several degrees
- Appliances on standby—routers, game consoles, computers—generate heat continuously without producing anything useful
- The dryer and dishwasher emit heat and moisture; it’s best to run them at night
- Outdated lighting: Incandescent or halogen bulbs dissipate most of their energy as heat, whereas LEDs do not
Shift cooking and appliance use to the evening, turn off devices rather than leaving them on standby, and opt for cold meals: these actions cost nothing and add up.
Plants: a real but slow effect
Vegetation cools the environment through evapotranspiration: the leaves release water vapor, which lowers the temperature of the surrounding air. This effect is well documented at the urban scale, where planted areas are significantly cooler than hard surfaces.
At the level of a single home, expectations should be realistic. A few houseplants won’t transform an overheated room. On the other hand, outdoor vegetation that shades a facade or a patio addresses the real issue—solar radiation—and that’s where the benefit becomes significant.
What really works, in order of effectiveness:
- A tree or a green pergola that shades a south- or west-facing facade
- Climbing plants on a wall or balcony, which limit heat buildup in the masonry
- Planters on a terrace, which cool the air before it enters through openings
- Houseplants, last on the list: pleasant, but with only a marginal thermal effect
The same reasoning applies on a neighborhood scale, where mineral surfaces accumulate heat during the day and release it at night, which explains why an urban center remains warmer than its outskirts.
Cooling the person rather than the room
This is the most effective method—and the one people talk about the least. All the previous methods have one thing in common: they attempt to cool several dozen cubic meters of air so that one or two people feel more comfortable.
But what matters isn’t the room temperature—it’s your body temperature. Acting directly on your body requires a fraction of the energy and produces faster results.
Immediate steps
- A lukewarm shower rather than a cold one: ice-cold water causes blood vessels to constrict, which then limits heat dissipation
- Wet the back of your neck, wrists, and forearms—where blood flows close to the skin—without wiping yourself dry afterward
- Drink water regularly; otherwise, sweating can no longer do its job
Fabrics designed for this purpose
A cooling garment works on the same principle as a damp cloth, but in the right place and with just a few dozen grams of water instead of several liters. A women’s Anti-UV cooling T-shirt from JadeCool™ works on contact with the skin, where heat is generated.
Other items work without any water at all. The EVO PhaseCool™ cooling armbands absorb heat by changing states, which avoids adding moisture to an already stuffy environment—precisely the drawback of a wet sheet.
For outings and outdoor activities, a PolyCool™ cooling cap or a PolyCool™ anti-UV cooling hat protects your head—the area that heats up first. Cooling towels complete the set by placing them on the back of your neck; simply apply and re-moisten as needed.
Insulation and Renovations: The Sustainable Solution
If your home becomes unbearable every summer despite all these measures, the problem is structural. A poorly insulated roof, an uninsulated attic, large west-facing windows without protection: no fan can make up for that.
Insulating the roof and attic is usually the first step, since that’s where most of the summer heat enters. External sunshades come next. These projects require a professional assessment, not a blog post, but it’s important to consider them rather than applying quick fixes every summer.
Signs that indicate you need renovations rather than temporary fixes:
- Attic rooms become uninhabitable as soon as the first hot day arrives
- The indoor temperature doesn’t drop even after a night of ventilation
- Large windows facing west, with no exterior protection
- The home was already difficult to heat in the winter: it’s the same insulation issue working both ways
Don’t miss: Cold, rain, heat waves… The guide to clothing for year-round gardening
When air conditioning is still the right solution
It would be dishonest to claim that we can always do without it. Certain situations fully justify its use: the presence of the elderly, infants, or frail individuals; medical conditions exacerbated by heat; or a home that is structurally uninhabitable while awaiting repairs.
In these cases, there is a consensus on two guidelines. Setting the temperature too low consumes a great deal of energy for only a marginal gain in comfort, and too sharp a temperature difference between indoors and outdoors is hard on the body: aiming for around 26 °C remains the standard recommendation. And air conditioning does not replace the measures mentioned above; it works best when heat has been blocked from entering in the first place.
To learn more: Heat Waves at Work: How to Stay Productive Without Putting Yourself at Risk?
We’re often asked if clothing can replace air conditioning. The honest answer is no—they’re not on the same scale. But the real question is this: why cool thirty cubic meters of air when it’s a person who’s hot?
— Édouard Castaignet, co-founder of G-Heat
Why Choose G-Heat for a Summer Without Air Conditioning
G-Heat has been designing thermal regulation equipment since 2017. Our stance on this issue is simple: we do not claim to replace air conditioning, and we will not let anyone believe otherwise. A piece of clothing affects a person; an air conditioner affects a volume of air.
What we offer is the complementary solution that most guides overlook, featuring technologies whose mechanisms are explained on each item. Some are activated with water; others operate entirely without water, which makes all the difference in an already humid indoor environment. The entire collection can be found in our cooling clothing and cooling accessories, with detailed information on the product lines available in our cooling T-shirts and cooling caps and hats.
Conclusion
Staying cool without air conditioning comes down to a matter of priorities. First, prevent heat from entering by using shutters and exterior insulation. Next, ventilate smartly—at night and by creating cross-drafts. Then reduce the heat you generate yourself, from cooking and appliances.
And finally, the strategy that almost no one uses: focus on the person rather than the room. It’s the only one where the cost remains negligible compared to the perceived benefit.
Whatever the weather. G-Heat, in all weather conditions.
Frequently Asked Questions
Should you open or close the windows when it’s hot?
Close them during the day—including the shutters—as soon as the outside air is warmer than the inside air. Open them wide at night and early in the morning, when the outside temperature has dropped, to let the accumulated heat escape.
Does a fan really cool a room?
No, it doesn’t cool the air; it speeds up the evaporation of your sweat. It cools you, not the room. In an empty room, it serves no purpose and even slightly warms the air with its motor.
Does hanging damp laundry in front of the window work?
Yes, through evaporation: as water turns into vapor, it draws heat away. There are two caveats, however: the humidity in the room increases, and air must be circulating for the process to continue.
Can cooling clothing replace an air conditioner?
No, and they’re not on the same scale. An air conditioner treats a volume of air, while clothing affects a single person. On the other hand, to achieve the same level of comfort, cooling a person requires infinitely less energy.
Do plants really cool a home?
They cool through evapotranspiration, with a very real effect on the scale of a garden or a city. Indoors, a few plants won’t make much of a difference. Vegetation that shades a building’s facade, on the other hand, works in the right way.
What temperature should you set the air conditioner to if you have one?
Around 26 °C, a widely recommended guideline. A lower setting consumes a lot of energy for only a marginal benefit, and too great a temperature difference from the outside is hard on the body.
How can you sleep better without air conditioning?
Air out the bedroom late at night, keep the shutters closed all day, use lighter bedding, and cool off just before bedtime with a lukewarm shower. A damp neck when lying down helps you fall asleep.
Sources and References
[1] “Extreme Heat and Heat Waves”, Santé publique France
[2] “France’s Adaptation to Climate Change”, Ministry of Ecological Transition
[3] “Working in the Heat: What You Need to Know”, INRS
[4] “Physical Activity and Extreme Heat: Mechanisms of Thermoregulation”, Weekly Epidemiological Bulletin, Santé publique France
[5] “Exercise-Induced Heat Stroke: A Medical Emergency”, Vidal
[6] “Ultraviolet Radiation”, Santé publique France
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