Heatwaves are set to hit parts of the UK over the next few days, with temperatures expected to reach as high as 33°C. Now, experts have shared whether doors and windows should be left open or closed during hot weather
It’s a question as old as time: Does leaving your doors and windows open during a heatwave actually make your house hotter or colder?
While many of us will be frantically opening our windows and turning on our fans, it can often feel as though we’re simply moving warm air around rather than cooling our homes. With certain parts of the UK anticipating temperatures of up to 33°C over the coming days, now’s the perfect moment to answer the question: is it better to keep your windows open or closed during a heatwave?
As someone residing in South-East England and preparing for the scorching heat, I was after a definitive answer. I consulted several experts, and their advice was unanimous: keep windows, doors, blinds, and curtains shut during the hottest periods of the day.
This method keeps your home sealed and reduces solar heat gain, which helps maintain cooler rooms. The experts also suggested opening windows and doors only early in the morning or late in the evening, when outdoor air is cooler than indoor air, to air out your home.
Tina Loveland, Senior Designer at Appeal Shading, the UK’s foremost supplier of smart powered blinds, bespoke conservatory blinds, insect screens and awnings, says: “Once sunlight has passed through a window and converted to heat inside a room, you’re fighting a losing battle. Blinds and shutters intercept that heat before it reaches your living space – which is proven to actually reduce heat build-up.
“A quality fitted blind on a sun-facing window can cut solar heat gain by 40-70%. Light-coloured or reflective fabrics work best – they bounce the energy back through the glass rather than absorbing it into the room. Dark blinds, by contrast, absorb heat and can actually make things worse.”
“Conservatories deserve a special mention too,” Tina adds. “Without roof blinds, they can hit 40°C or above during a heatwave, radiating heat downwards into the house. If you have conservatory blinds, you need to make sure you keep these closed.”
Throwing open your windows during a heatwave feels like the obvious solution. Yet, according to Tina, this is actually the wrong move.
She explains: “It seems counterintuitive at first, but there’s a really simple rule you can follow that puts it into perspective: if it’s hotter outside than inside, opening your windows will warm your home up, not cool it down.
“During a UK heatwave, outdoor temperatures can stay above 30°C from mid-morning until early evening. If your home is sitting at 24°C or 25°C, cracking a window will actually just let hotter air in.”
Both NHS and Public Health England guidance backs this up: keep windows in rooms that are in direct sunlight firmly shut during the hottest part of the day. The aim is to treat your home like a cool box – sealed and shaded until outdoor temperatures eventually begin to fall.
That said, once the evening brings cooler temperatures, you can fling open your windows and blinds to welcome in the fresh air. Tina explained: “Once outdoor temperatures fall below what’s inside – usually from around 9pm or 10pm in the peak of summer – that’s when you should open your windows and blinds to let cooler air in and hotter air out.
“Open up fully, ideally on opposite sides of the house to create a cross-draught, and let the cooler air flush out the heat that’s built up throughout the day.”
Max Wilson, co-founder of Pocket Storage, largely echoes this view, recommending you treat your home like a fridge between 10am and 6pm by keeping everything shut on the sunny side.
“Opening your windows will either cool or warm up your house depending on how warm it is outside,” he points out. “The major mistake most homeowners make is opening all their windows and doors for the entire day. The problem is, opening windows and doors when it is warmer outdoors is no different from opening a door to an oven.
“Houses in Britain are constructed in a way that conserves heat rather than repels it. All of our insulating materials, furniture, carpets, bedding, even the walls of our homes, absorb heat all day long and then release that heat during the evening.
“The best solution is to adopt the ‘lockdown and flush strategy.’ Between 10am and 6pm, when the sun is at its most powerful, keep all the windows, doors, drapes, and blinds closed on the side of the house facing the sun. Think of your house as a fridge, and during the day, your goal is to retain the cold air.
“In contrast, during the evening when temperatures begin to lower starting around 7 o’clock, the flushing stage begins. For this, open windows that face each other on the opposite sides of the building and leave interior doors open to provide ventilation. This means letting out the heated air from the day and bringing in fresh, cool air. If possible, opening windows at night will provide more cooling.”
Max also recommends removing clutter, furniture, laundry and storage boxes from around windows and doors to help air circulate freely. Cluttered hallways and blocked pathways can restrict airflow, leaving homes feeling stuffy and uncomfortably warm.
His key piece of advice is to ensure there’s a clear route between the opposite windows to allow air to flow properly.
He added, “Ultimately, it is not only about reducing the temperature of a house after it becomes very hot but rather preventing the temperature from rising in the first place. By closing windows when it is extremely hot and opening them when cooler air comes around and ensuring good circulation in the house, people can significantly cope during a heatwave.”
John Klee, a heating technology expert at BestHeating, agrees that keeping windows, doors and blinds shut during hot weather is “vital” for maintaining cool rooms and stopping outdoor heat from being absorbed by floors, furniture and walls. He also recommends investing in thermal or blackout blinds and placing an ice-filled bowl in front of a fan to generate a refreshing breeze.
He explained: “Whilst many people look forward to the brightness that the summer weather brings into their homes, keeping doors and windows closed and blinds down during heatwave periods is a vital way for preventing rooms from becoming uncomfortably hot. In doing so, it blocks out the sun’s rays, maintaining the coolness of the air inside rooms and avoiding heat from the outdoors from being absorbed by floors, furniture and walls.
“There are various household tricks that can be used in addition to make hot weather more manageable. Many rely on fans in the UK to keep their rooms cool in the summer, but placing a bowl of ice in front of these can increase their effectiveness, circulating a cool breeze around a room rather than redistributing the same warm air.
“For even greater protection against the heat, households can invest in thermal or blackout blinds, which are designed to limit the amount of warm air and sunlight entering a room. This can be particularly beneficial during heatwaves, when high indoor temperatures often make it difficult to sleep comfortably. Aside from this, ensuring that radiators are properly switched off in every room ensures that spaces aren’t unnecessarily being heated up or counteracting the cooling measures being used.”
Edward Simon, director at Direct Fabrics, stressed that preventing heat from entering through windows in the first place is far easier than attempting to cool a room that has already absorbed the sun’s rays. He suggested fitting blinds as close to the window frame as possible to reduce the “chimney effect,” whereby warm air circulates between the glass and the fabric.
He also recommended layering window coverings and opting for reflective linings to better manage heat.
“Start by stopping heat at the window, because it’s far easier than trying to cool a room after it’s already absorbed sun,” he says.
“Fabric choices and how they’re fitted make a noticeable difference here. Light-coloured blinds or curtains (especially on the window-facing side) reflect more solar energy than dark fabrics, and a tighter weave reduces how much heat and glare make it through. Where possible, a reflective or blackout lining helps cut solar gain before it spreads into the room, particularly on large or sun-facing panes.
“The set-up is just as important as the textile. I’d pay attention to gaps, because warm air can circulate between the glass and the fabric and then spill back into the room. Fitting blinds close to the frame, using a snug recess fit where you can, and adding a pelmet or a well-fitted header all reduce that “chimney effect” down the window. In east and west-facing rooms, which get low, intense sun, having a pale, reflective surface facing the glass is especially helpful. Layering can also give more control on changeable UK days, for example, a voile to soften glare without darkening the room, paired with a lined curtain you close during the hottest hours.
“Timing ties it all together. Keep sun-facing coverings closed by late morning, ideally before the sun is fully on the glass, and keep windows shut while it’s hotter outside than in. Later, once the outdoor air is genuinely cooler, switch to purge ventilation by opening windows on opposite sides of the home to pull cooler air through. If the house allows it, a higher window or an upstairs opening helps, too, because hot air collects near ceilings.
“Use internal doors deliberately. During the day, close off the hottest, sun-exposed rooms to stop heat drifting into cooler spaces. At night, open internal doors again so the whole house can clear stored heat. Finally, it’s worth reducing indoor heat sources during peak hours, such as long oven cooking, tumble drying or running multiple heat-producing appliances, because those extra gains can tip a warm home into an uncomfortable one.”
Darren Coates, sales director at SolarFrame, warned that leaving windows and doors open during hot weather can “absolutely make your house hotter, especially if you’re doing it in the middle of the day when the weather outside is at its hottest”.
He explained that many people mistakenly believe they’re ‘letting air in’, when in reality, if the outside air is warmer than inside the house, opening a window simply allows hot air to flood in.
For those with good double or triple glazing, the glass should slow heat transfer, meaning you’re far better off keeping windows and external doors firmly shut during the hottest spells. That said, Coates also recommended throwing windows and external doors open early in the morning or late in the evening, once temperatures have dropped.
To make this more effective, he suggests opening windows on opposite sides of the property early in the morning to create proper cross-ventilation, then closing them before temperatures rise. He added: “As well as this, don’t leave patio doors, French doors or bi-folds wide open all afternoon if the heat outside is high, because that heat will come straight inside.”
Darren also warned that conservatories can rapidly become scorching hot, essentially transforming into “greenhouses”. He advises sealing them off from the rest of the property during daytime hours and points out that fitting a solid tiled roof is the most effective way to keep conservatories cool.
He explained: “Conservatories are the worst offenders. A glass or polycarbonate roof can turn the room into a greenhouse, and if you leave the doors between the conservatory and the house open, that heat spreads into the rest of the home.
“Keep the conservatory shut off during the hottest part of the day, ventilate it when it’s cooler, and if it’s a room you can’t use every summer, then the roof is usually the real problem. Swapping an old glass or polycarbonate roof for a solid tiled roof will make far more difference than just opening another window and hoping for the best.
“A simple rule to follow: If it’s hotter outside than inside, keep windows and doors closed. Once it cools down outside, open them up and get the air moving”.
Martyn Bridges, director of external affairs at Worcester Bosch, offered comparable guidance, recommending that householders keep windows, blinds and curtains shut during the hottest periods of the day to block out the sun and prevent rooms from getting excessively warm.
He explained that this helps minimise solar gain, which occurs when the sun heats the home and causes indoor temperatures to climb.
He added: “Another great way to help manage indoor temperatures is to use natural ventilation strategically. Once the sun has gone down, and if it is safe and secure to do so, opening windows at opposite ends of the property can help create a through draught.
“This encourages warmer, stale air to move out of the home while allowing cooler evening air to circulate, helping to make the property feel more comfortable after a hot day.
“So, the best approach is to keep windows, blinds, and curtains closed during the day to limit heat build-up, then open windows in the evening once the temperature outside has dropped and it is safe to do so.”
What else can people do to keep their homes cool during a heatwave?
Martyn explained: “During a heatwave, the key is to stop the home from heating up too much during the day, then use natural ventilation later when outside temperatures begin to fall. Some of the most effective steps are also the most budget-friendly, as they focus on managing sunlight, airflow and the heat already being generated inside the home.
“The most successful form of technology to cool a property is an air conditioning unit or an air-to-air heat pump. These products are quite often used to supplement a heating system by having one or more indoor convector units connected to an outdoor unit. The indoor units then blow chilled air into the property cooling down the rooms and areas where they are sited.
“Fans can also help move excess heat around the room. A slightly more unusual but commonly suggested tip is to place a bowl of ice in front of a fan, so cooler air is blown around the space. This can be a useful short-term option for people looking for a simple cooling method without investing in a larger system.
“Another simple and budget-friendly step is to turn off household appliances when they are not in use. Appliances left on standby can still generate heat, so switching them off can help reduce unnecessary warmth indoors during hot weather.”
