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Heat German-style with two habits: air the rooms fully for five to ten minutes two or three times a day with the radiator off (Stosslueften), and never leave windows tilted — a tilted window barely exchanges air but cools the wall all day. Keep every room at 16 °C or more, leave a hand’s width between furniture and exterior walls, and remember the radiator dial is a target temperature, not a power setting: 3 means roughly 20 °C. Done right, this prevents both mould and the surprise heating bill in spring.
Two habits decide how your German winter goes: how you heat, and how you air. Get them wrong and you face a heating bill that surprises you in spring — and possibly a mould discussion at move-out.
This is not a lecture. German houses are built and insulated differently from most American homes, and nobody explains the consequences at in-processing.
Why a tilted window costs money
The tilt position (Kippstellung) feels like sensible ventilation. It is the opposite. A tilted window exchanges very little air, but it continuously cools the wall around the frame — and the radiator underneath runs against it all day.
The German method is Stoßlüften: open the window fully, five to ten minutes, twice or three times a day, radiator off during that time. The air is exchanged completely, the walls stay warm, and the room is back to temperature within minutes.
Even better in winter is Querlüften — opposite windows open at the same time for a few minutes. Faster, and less heat lost from the structure.
Where mould comes from
Mould is not dirt. It is condensation: humid air meets a cold surface, water settles, and spores do the rest. Showering, cooking and drying laundry indoors all add moisture — a household produces several litres of water vapour a day.
The places to watch: outside corners of rooms, behind wardrobes standing against exterior walls, window reveals, and bathrooms without a window.
What helps:
- Air after every shower and after cooking — fully open, briefly.
- Leave a hand’s width between furniture and exterior walls.
- Do not let rooms cool below roughly 16 °C, including bedrooms and unused rooms.
- Dry laundry outside or in a well-aired room, not in a closed bedroom.
This matters beyond comfort: if mould appears and the cause is found to be ventilation behaviour, it can become a deposit issue at move-out.
What the numbers on the radiator mean
The dial on a German thermostatic valve is not a power setting — it is a target temperature. Roughly: 3 ≈ 20 °C, each step about 4 degrees. Turning it to 5 does not heat the room faster; it just overshoots and then costs more.
The snowflake symbol is frost protection — it keeps the room around 6 °C so pipes do not freeze. Never turn radiators fully off in winter, even in rooms you do not use.
Why this shows up on your bill
Heating costs are part of the Nebenkosten you pay monthly as an advance. Once a year they are settled against actual consumption. Heating well through the winter is not just comfort — it is the difference between a refund and a bill in spring.
Status September 2026, no warranty.
Next: Setting up utilities · Your German lease explained · Moving out and getting your deposit back
FAQ
Frequently asked questions
Why should I not leave windows tilted in a German home?
A tilted window exchanges very little air but continuously cools the wall around the frame — while the radiator underneath runs against it all day. The German method is Stosslueften: open the window fully for five to ten minutes, two or three times a day, with the radiator off during that time.
Where does mould in German houses come from?
It is condensation, not dirt: humid air meets a cold surface. A household produces several litres of water vapour a day through showering, cooking and drying laundry. Watch outside corners, the space behind wardrobes on exterior walls, window reveals and bathrooms without a window.
What do the numbers on a German radiator mean?
The dial is a target temperature, not a power setting: 3 means roughly 20 °C, and each step is about 4 degrees. Turning it to 5 does not heat the room faster — it overshoots and costs more. The snowflake symbol is frost protection at around 6 °C; never turn radiators fully off in winter.
How warm should unused rooms be kept in winter?
Do not let any room cool below roughly 16 °C, including bedrooms and rooms you do not use. Cold rooms mean cold walls, and cold walls are where condensation and mould start. Leave a hand's width between furniture and exterior walls.
Can heating habits affect my deposit?
Yes. If mould appears and the cause is found to be ventilation behaviour, it can become a deposit issue at move-out. Heating and airing correctly is also the difference between a refund and a bill when the annual Nebenkosten statement arrives in spring.
