As temperatures in parts of the UK are set to reach up to 33°C, the age-old question resurfaces: should you open or close windows during a heatwave? Experts have weighed in, and their advice is unanimous—keep windows, doors, blinds, and curtains shut during the hottest periods of the day.
Why Closing Windows Works
According to Tina Loveland, Senior Designer at Appeal Shading, once sunlight passes through a window and converts to heat inside a room, it becomes difficult to cool down. Blinds and shutters intercept that heat before it enters your living space, reducing heat build-up by 40-70%. Light-coloured or reflective fabrics work best, as they bounce energy back through the glass rather than absorbing it into the room. Dark blinds, on the other hand, can absorb heat and worsen the situation.
Conservatories deserve special attention, as they can reach 40°C or more during a heatwave, radiating heat downward into the house. Keeping conservatory blinds closed is essential.
The 'Lockdown and Flush' Strategy
Max Wilson, co-founder of Pocket Storage, recommends treating your home like a fridge between 10am and 6pm by keeping everything shut on the sunny side. Opening windows when it's hotter outside than inside is akin to opening a door to an oven. British homes are built to conserve heat, so insulating materials, furniture, and walls absorb heat all day and release it in the evening.
The best approach is the 'lockdown and flush' strategy: from 10am to 6pm, keep windows, doors, drapes, and blinds closed on the sun-facing side. In the evening, when temperatures drop (around 7pm), open windows on opposite sides of the building and leave interior doors open to create cross-ventilation, flushing out heated air and bringing in cool air. Removing clutter from around windows and doors helps air circulate freely.
Expert Tips for Staying Cool
John Klee, heating technology expert at BestHeating, agrees that keeping windows, doors, and blinds shut is vital. He also suggests placing a bowl of ice in front of a fan to circulate a cool breeze, and investing in thermal or blackout blinds. Ensuring radiators are switched off in every room prevents unnecessary heating.
Edward Simon, director at Direct Fabrics, emphasises that preventing heat from entering through windows is easier than cooling a room that has already absorbed sunlight. Light-coloured blinds or curtains with a tighter weave reduce heat and glare. Fitting blinds close to the frame reduces the 'chimney effect' where warm air circulates between glass and fabric. Layering window coverings, such as a voile paired with a lined curtain, offers more control.
Timing is Everything
Darren Coates, sales director at SolarFrame, warns that leaving windows open during the day can make your house hotter. With good double or triple glazing, glass slows heat transfer, so keeping windows shut during the hottest spells is better. Open windows early in the morning or late in the evening to create cross-ventilation, then close them before temperatures rise. Conservatories can become greenhouses; seal them off from the rest of the house and consider a solid tiled roof for better insulation.
Martyn Bridges, director of external affairs at Worcester Bosch, recommends keeping windows, blinds, and curtains shut during the day to minimise solar gain. In the evening, open windows on opposite sides to create a through draught, allowing cooler air to circulate. He also suggests using air conditioning units or air-to-air heat pumps for effective cooling, or placing a bowl of ice in front of a fan for a simple cooling method. Turning off household appliances when not in use reduces unnecessary heat generation.
Conclusion
The simple rule: 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. By following these expert tips, you can keep your home cooler during a heatwave without relying solely on fans or air conditioning.
