With this weather, you may want to do everything you can to protect yourself from the cold and prevent energy costs from skyrocketing. According to Van Meegeren, that just doesn’t make sense: “Ventilation costs energy, but it’s not a waste of energy, because you need it for healthy air in the house.”

Good ventilation

“Research shows that the air in many bedrooms is unhealthy due to insufficient ventilation,” says Van Meegeren. Opening the window helps, of course, but with these temperatures it causes cold in the house.

You also waste a lot of energy if you turn on the heating with the window open. So don’t do that. “I sleep with an extra blanket myself,” says Van Meegeren. If you open the window slightly, it will freeze not only in your room. “It may be 10 degrees, but there won’t be much frost in your house. »

If you live in a modern house with mechanical ventilation, you can possibly leave the window closed, explains Atze Boerstra, professor at TU Delft and director of BBA Indoor Environment. But: “If you have the window open, you get more fresh air than with mechanical ventilation alone.”

Sleep quality

An open window also helps with your sleep. Good ventilation has a direct influence on the quality of your sleep. Jelle Laverge, lecturer in building physics at Ghent University, has researched this. “To feel well rested the next day, good air quality is important. Sleeping with the window open helps.”

You also fall asleep more easily at a lower ambient temperature. “To fall asleep, you need a slightly cooler environment to bring down your core body temperature,” says Laverge. “We also cover up better when we sleep, so the temperature can drop a bit.”

“We see quite consistently that people who sleep in a room with good air quality report themselves in the morning as having slept better and feeling better rested,” says Laverge.

Fogged windows

With these temperatures, you also see a lot of fogged up windows. It has to do with single glazing and the humidity that people give off. Boerstra explains: “Moisture condenses on the cooler surfaces of the room. With single glazing, these are the windows.

In the longer term, this could also lead to fungus. “It runs down the glass and collects at the bottom of your window,” Boerstra says. “Mold is the last thing you want in your bedroom. It releases mold spores and you breathe them in while you sleep. It’s unhealthy.”

Does the open window still carry risks?

“A fully open window is very enthusiastic with these temperatures,” says Peter Luscuere, professor at TU Delft. Hoewel het goed is voor de verse lucht om het raam op een kier te zetten, wijst Luscuere er ook op dat de lucht van buiten niet altijd gezonder is dan de lucht binnen: “In de buurt van een industriewijk is de lucht binnen vaak beter dan outside.”

If it’s raining very hard and the wind is blowing directly at your window, that could also cause leaks, according to Van Meegeren of Milieu Centraal. “But that doesn’t happen very often.”