It is well known that proper ventilation is important. But how do you deal with it in very cold temperatures? The 5×5 rule can help you with this.

Proper ventilation in the house or apartment is important to prevent mold and create a healthy indoor climate. Ventilating the room several times a day is usually no problem at all, because you quickly notice that the fresh air in the room is really good for you.

But how do you ventilate properly when it’s extremely cold outside? Cold, snow and ice are currently keeping Germany in its grip, and as soon as the window is open, the biting cold fills the room. The Window Façade Association recommends the following rule of thumb for manual ventilation:

The 5×5 rule will help you and if that doesn’t work, the 3×5 rule will do as well.

Word has gotten around that it’s better not to open windows for a long time, but rather to open them fully and then air them briefly. This is then called intermittent ventilation or, if you open opposite windows, cross ventilation.

In spring or autumn, a complete air exchange can take 15 to 20 minutes and if you do this three to five times a day, the windows are open for quite a long time. This tactic no longer works in winter because the outside temperatures are too low.

However, it is advisable to air the room just as often, i.e. three to five times a day even when the temperature is below zero. However, three to five minutes with the window open are then sufficient. From this, the 5×5 rule can be derived as a reminder: Translated, this means airing the room five times a day for five minutes.

This is easy to keep on holiday or at the weekend or if you work a lot from home. However, if you are not at home during the day, you need a different strategy. The good news: If you are absent all day, less frequent airing is sufficient. Minimum morning and evening, but better use the 3×5 rule. That means airing the room for five minutes three times a day.

Air out in the morning when you get up from work and again just before you go to bed.

Of course you can make a ventilation plan and maybe even set a timer to remind you to open the windows every few hours.

The experts from the trade association advise: “You should ventilate when it is necessary and only for as long as necessary. In addition to your personal feeling, a hygrometer can help here. Ventilation is required from an air humidity of more than 60 percent”.

Thermo-hygrometers are available in analog and digital form and are also available in hardware stores for little money. Alternatively, there are also smart home solutions that you can use to keep an eye on the humidity.

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