A few years ago, a building contractor told me a story that scared me enough to change my habits:
“I worked with a young couple recently who fully remodeled an old house. They both worked full-time. Every morning, they both got up, took showers, got dressed and left for work, to return again late in the evening. Within three months, mold had taken over in multiple rooms of their house and they spent a fortune to have the problem fixed. Not once in those three months did they air out after taking a shower, and all the moisture just built up in there.”
After hearing this story, you can bet I open the windows and air out the bathroom after a shower! And for good air quality in your house, to prevent mold, and to increase heating efficiency in the winter, you should also air out (lüften) your home regularly.
German buildings are not typically built with extensive ventilation systems and don’t use forced-air heat the way many homes in the US do. Most buildings here are fairly air-tight and have no ventilation except the windows and doors, and heat is radiant, whether from radiators or in-floor heating.
According to the brochure available online from the Verbraucherzentrale Energieberatung, a four person household will create about twelve liters of moisture per day. Regularly opening your windows and airing out your apartment will regulate the humidity inside – and should be done two to four times daily, plus after showering, cooking, or mopping the floors.
German windows are fantastic: they open fully for easy cleaning, and they have the “kipp” (tilt) mechanism which allows you to let just a little air in. However, when you are doing your big lueften, you should open the windows all the way – opening them just a crack will actually cause condensation around the window and could cause mold. Plus, getting a full exchange of air in a few minutes’ time by opening all the windows is a more efficient energy use than leaving a window cracked and letting the heat escape over a longer period of time.
So as you head into this winter, keep in mind that a healthy house is an aired-out house, and keep things fresh instead of stuffy!