Sometimes your first instinct to keep homes cool might not have the effect you intended
Your first instinct might not be the best idea(Image: © 2020 Grace Cary)
With yet another piping hot day forecast on Sunday, millions of people up and down the UK will be looking for ways to keep their homes cool. Yet one of the most common habits during a scorching heatwave could be having the opposite effect.
Throwing open the windows as soon as temperatures begin to climb may feel like the obvious thing to do. However, experts say doing so during peak hours – between 11am and 6pm – when the air outside is often hotter than the air inside, can actually warm up homes instead of cooling them down.
When outside air is warmer, opening windows allows that heat to flow into your home. Rather than creating a cooling breeze, it can act more like a convection oven, trapping warm air inside and making rooms increasingly uncomfortable.
Instead, homeowners are advised to keep their windows firmly shut during the hottest part of the day, particularly those on the side of the home facing direct sunlight. According to the Energy Saving Trust (EST), closing curtains or blinds at the same time helps block solar heat from entering through the glass, preventing rooms from heating up even further.
The EST recommends opening windows when the outside air is cooler than the temperature indoors, such as late in the evening, overnight or early in the morning. Doing so allows cooler air to circulate through the property and helps remove heat that has built up during the day.
Opening windows on opposite sides of the house can create a cross-breeze, improving ventilation and helping cooler air move through the property more effectively. The Energy Saving Trust also suggests opening internal doors where possible to encourage airflow between rooms.
The UK Health Security Agency (UKHSA) advises reducing additional heat inside the home by limiting the use of ovens and other appliances that generate unnecessary warmth during the hottest parts of the day. Keeping electrical devices switched off when they are not needed can also help minimise excess heat.
Fans can help people feel cooler, but they work best once the temperature outside has started to fall and cooler air is able to circulate through the home. The UKHSA says fans should not be relied upon as the primary cooling method once indoor temperatures exceed 35C, making overnight ventilation particularly important during prolonged hot weather.
While it may seem counterintuitive, keeping windows and curtains closed on the sunny side of the house during the hottest hours before ventilating the property overnight is among the measures recommended by experts to help keep indoor temperatures down during periods of extreme heat.