With another scorching hot day forecast for Sunday, millions across the UK are seeking ways to keep their homes cool. However, a common habit during heatwaves may be counterproductive.
Common Mistake: Opening Windows During Peak Heat
Throwing open windows as temperatures climb seems obvious, but experts warn that doing so between 11am and 6pm, when outside air is often hotter than indoor air, can actually heat homes. The Energy Saving Trust (EST) explains that opening windows allows warmer outside air to flow in, acting like a convection oven and trapping heat inside.
Expert Advice: Keep Windows Shut, Use Curtains
Homeowners are advised to keep windows firmly shut during the hottest part of the day, especially on sides facing direct sunlight. The EST recommends closing curtains or blinds to block solar heat from entering through glass. This prevents rooms from heating further.
When to Ventilate
The EST suggests opening windows when outside air is cooler than indoors—late evening, overnight, or early morning. This allows cooler air to circulate and remove built-up heat. Opening windows on opposite sides of the house creates a cross-breeze, improving ventilation. Opening internal doors also encourages airflow between rooms.
Reducing Indoor Heat Sources
The UK Health Security Agency (UKHSA) advises limiting use of ovens and other heat-generating appliances during the hottest hours. Keeping electrical devices switched off when not needed also minimizes excess heat.
Using Fans Effectively
Fans help people feel cooler but work best once outdoor temperatures drop and cooler air circulates. The UKHSA warns that fans should not be the primary cooling method when indoor temperatures exceed 35°C, making overnight ventilation crucial during prolonged hot weather.
While counterintuitive, keeping windows and curtains closed on sunny sides during peak hours, then ventilating overnight, is recommended by experts to maintain lower indoor temperatures during extreme heat.
