How to ventilate your home during a heatwave
Your home is not a passive box. Opened and closed at the right hours, it can stay several degrees cooler than the street.
Most homes without air conditioning have more room to manoeuvre than people think. The difference between a flat that stays bearable and one that becomes an oven is rarely the building itself. It is timing: which hours you open, which hours you shut, and what you do about the sun hitting the glass.
The one rule underneath everything
Open when the air outside is cooler than the air inside. Close when it is warmer.
That sounds obvious, but it is the opposite of what most people do. The instinct on a hot day is to throw the windows open for fresh air. At 3 pm in a heatwave, that instinct actively heats your home. Every hour a window stands open against 35 °C air, your rooms move closer to 35 °C.
The corollary matters just as much: when the outdoor temperature finally drops below your indoor temperature, usually well after sunset, that is your window of opportunity. It may only last a few hours, and it is the only free cooling you get.
Three things to get right
Shading. Sun coming through glass is a much bigger heat source than warm air leaking in. Blocking it outside the window is far more effective than blocking it inside. See protecting your windows from the sun.
Timing. The pattern over a heatwave is not a single decision but a daily rhythm of keeping heat out, flushing heat at night, and holding the cool you gained. See the three phases of heat.
Airflow. Where you put a fan depends entirely on whether your home has windows on one side or on opposite sides. The right placement moves a lot of air. The wrong one just makes noise. See where to place a fan.
Your layout sets the ceiling
A flat with windows on two opposite façades can be flushed of hot air in minutes once outdoor air is cooler, because air has somewhere to go. A single-sided flat, with all its windows on one façade, has no natural through-draught and depends much more on fan placement and patience.
Neither is a lost cause. But knowing which one you have changes what you should do, and it is the first thing to work out before you start moving fans around.
Safety first
None of this replaces medical judgement. If someone is showing signs of heat exhaustion, confusion, or heatstroke, ventilation advice is not the priority. Follow your local health agency’s guidance and get help.
In this guide
The three phases of heat in your home
A heatwave is not one long problem but three, and each has its own answer. Keep heat out, cool down, then hold what you gained.
How to protect your windows from the sun
Sunlight through glass is the biggest source of daytime heat in most homes. Blocking it outside the window beats anything you do inside.
Where to place a fan in a single-sided or cross-ventilated home
A fan does not cool air, it moves it. Where you put it depends entirely on whether your windows are on one façade or on opposite sides.
Why your home stays hot after a heatwave
The forecast dropped ten degrees and your flat did not. Walls, floors, and furniture store heat and give it back for days.
Common questions
- Should I open my windows during a heatwave?
- Only when the outdoor air is cooler than the air inside. During the hottest part of the day, opening windows brings hot air in and makes the room warmer. Once the outdoor temperature drops below your indoor temperature, usually in the evening or overnight, open as wide as you safely can.
- Does closing the shutters really make a difference?
- Yes, and it is usually the single biggest change you can make. Sunlight passing through glass is the main source of daytime heat gain. Blocking it on the outside, with shutters, blinds, or an exterior screen, stops the heat before it reaches the room.
- Does a fan cool a room?
- No. A fan does not lower the air temperature. It moves air, which helps sweat evaporate so you feel cooler, and it can push hot air out or pull cool air in when it is placed at a window. In a closed empty room it slightly warms the air.
- Why is my flat still hot when the heatwave is over?
- Walls, floors, and furniture store heat during the hot days and release it slowly afterwards. Well insulated homes hold it longest. Keep ventilating at night for a few more days and the stored heat will work its way out.
These guides are informational and are not medical advice. If heat is making you unwell, follow your local health agency’s guidance.
Updated