Is it best to keep windows closed in hot weather?

To keep windows closed in hot weather might appear counterintuitive. With many of us searching for the best ways to cool down the house, here's why you should keep them firmly closed this summer.

We're all looking for ways to keep our house cool this summer, whether it's investing in a fan or swapping your bed sheets. And as temperatures soar, the weather is bringing other challenges too, such as how to get to sleep in the heat and how to cool a baby down in hot weather.

Opening your windows might seem like the natural thing to do when it gets hot outside, but it's not always an effective way of keeping your home cool. Here's everything you need to know about when and why you should keep windows closed in hot weather.

Is it best to keep windows closed in hot weather?

Yes, to keep your house cool you should close the windows when it is hot outside, according to nidirect. They add that it's best to have pale coloured curtains in your home, because dark curtains or metal blinds can make homes hotter.

However, deciding whether you should have your windows open or closed during the heat depends on different factors - such as how warm it is outside compared to inside your home, how well insulated you home is and how much direct sunlight is on you window. 

NHS Property Services recommends "closing blinds and curtains in rooms that face the sun, opening windows on the side of the building that is in the shade, and closing windows that are in direct sunlight." They add that you should "keep the windows closed if you have air conditioning so that cooler air can circulate."

Woodbridge Home Solutions advises that keeping windows closed in the heat is only effective in well-insulated homes. In homes with insufficient attic and wall insulation, it may be a better idea to open the widows throughout the day when it gets too hot indoors.

What temperature to close windows?

Though there's no set temperature, you should keep your windows closed when it is cooler inside than outside. The best way to monitor this is by using two thermometers - one designed to read the room temperature and one for measuring the outside temperature.

If you want to air out your home, the best time of day to do this is early in the morning, before it gets too hot, and to only open windows with no direct sunlight on them. 

The afternoon is the hottest time of the day, so windows should remain closed unless there is a strong breeze, in which case you can open the windows but keep the curtains closed. Lisa Slack, head of product at window furnishings company Thomas Sanderson, says "A lot of heat comes through the windows, so it’s important to keep your curtains drawn and your blinds down to create a dark room, but crack open the window to allow the air to circulate."

Should you open windows during the day in summer?

No, generally you should not open windows in summer if it is hotter outside than inside. You should also keep curtains and blinds closed, to further keep out the heat.

As with opening your windows, the best time to let any light in during the day is in the morning, before the temperature rises too much. Yvonne Keal, senior product manager at window-dressing company Hillarys, says "Early morning is the best time to let natural light into your home before the temperature gets too hot, so at this time you may want to partially open your window and let some light filter through your window dressings." 

However, later in the day, once temperatures are rising, it is best to keep windows closed. Keal adds, "Between 12pm and 4pm, when the sun is at its highest, it’s best to keep your blinds, curtains and windows closed. Closing your window during the hottest time of the day ensures as little heat as possible is entering your home and this is especially true for south facing homes, as they are naturally exposed to more sunlight and can experience higher temperatures inside."

It's also a good idea to keep internal doors open so that air can circulate through your home.

Should you open windows at night in summer?

The air is cooler at night, so you can open the windows. But nidirect says to make sure you close your downstairs windows when you leave the house or go to bed.

Yvonne Keal of Hillary's says "Once the sun goes in, you can open your windows so cooler air can circulate around your home, as temperatures tend to drop in the evening. Although, during an extreme heatwave the temperature outside may still be warmer than inside so it’s best to check first.”

If there is a breeze outside in the evening then keeping the windows may help you get to sleep. Other tips include using light, cotton sheets and keeping your feet out of the covers.

Foil on windows - heatwave hack:

Spreading out kitchen foil on windows will reflect the sun away from your house, and it's a lot cheaper than installing air conditioning.

However, it doesn't always work unless it's done correctly, so make sure the shinier side of the foil is facing towards the sun and cut the foil two to three inches bigger than the size of the window, so you have platy of room to secure it with masking tape. 

Other tapes can be used, but masking tape is best for avoiding damage to paintwork. You can add another layer of foil for extra insulation.

The advantage of using foil is that it's non toxic and can withstand temperatures of up to 660C, so you don't need to worry about it melting.

For more ingenious ways to cool down fast, we have some great ideas for you. How to keep cool during pregnancy can be even more difficult, but our expert guide offers expert and practical advice on the best methods to use. For those still hot at night and wondering if it's bad to sleep with a fan on, we weigh in on the pros and cons.