Heating, Lüften & Mold: How to Survive Your First German Winter in a Rental
Germans open their windows wide in December, even when it's freezing outside. It's not a strange habit, it's how you avoid mold, a fight with your landlord, and losing part of your deposit.
My first German winter, I did everything "right" by the standards of where I came from: windows closed, a little heating to save money, laundry drying on the rack in the bedroom. By February there were black spots in the corner behind the wardrobe. That's when I learned the word Schimmel (mold), and that in Germany, how you heat and air your flat is not just your business. It's part of your rental contract.
This guide explains how heating and airing (Lüften) really work in German apartments, what your duties as a tenant are, how to prevent mold, and exactly what to do if it appears anyway, so you protect your health, your wallet and your Kaution.
Why Mold Is Such a Big Deal in Germany
German buildings, especially renovated ones, are built to be very airtight to save energy. That's great for heating bills, but the moisture you produce every day (cooking, showering, breathing, drying laundry) has nowhere to go. A household of two can easily release several litres of water vapour into the air per day.
When that warm, humid air touches a cold surface, like an outside wall, a window frame or a corner behind furniture, it condenses. Wet surface plus a few days equals mold.
Your Duty as a Tenant: Heat and Air "Properly"
German tenancy law expects you to heat and ventilate your flat properly (ordnungsgemäß heizen und lüften). There's no single number in the law, but courts and tenant associations give a pretty clear picture:
How to Lüften Like a German
The German way is Stoßlüften: short, strong bursts of fresh air with windows wide open, instead of leaving one window tilted all day.
The routine
- 2 to 4 times a day, open the windows fully. Morning after waking up is the most important time.
- 5 to 10 minutes in winter is enough (up to 15 minutes in milder weather). The colder it is outside, the faster the air exchanges.
- Turn the radiator down while airing, then back up when you close the window.
- Even better: Querlüften (cross-ventilation). Open windows on opposite sides of the flat at the same time for a strong draught.
- Air right after showering, cooking or ironing, and keep the bathroom door closed while you do it so the steam goes outside, not into the rest of the flat.
Everyday Habits That Prevent Mold
- Leave a gap between furniture and outside walls, around 5–10 cm, especially for wardrobes and beds. Your landlord can't forbid you from placing furniture against outside walls, but a gap lets air circulate.
- Dry laundry outside or in the Trockenraum (drying room) if your building has one. If you must dry it inside, do it in a heated room with the door closed, and air more often.
- Wipe condensation off windows and the shower in the morning.
- Use lids when cooking and the cooker hood.
- Check hidden corners once a month: behind wardrobes, under the bed, window corners, behind curtains.
Who Pays for Heating?
In most rentals, heating is part of your Nebenkosten (utilities). You pay a monthly advance with your rent (that's why the Warmmiete is higher than the Kaltmiete), and once a year you get a statement (Nebenkostenabrechnung) based on your real consumption, measured by the meters on your radiators. Under the heating cost rules, at least half of the heating bill must be based on what you actually use.
That's why the end-of-year bill can be a shock: if you heated more than the advance covered, you pay the difference in one go. If your flat has its own gas boiler or a night storage heater, you pay the energy company directly instead.
And what the landlord must provide
During the heating season, usually from 1 October to 30 April, the heating must work well enough to reach around 20–22 °C in living rooms during the day and about 18 °C at night. If your heating is broken or too weak, report it in writing. A cold flat can justify a rent reduction.
You Found Mold. Now What?
Don't panic, and don't just paint over it. Follow these steps in order:
Rent Reduction (Mietminderung): What's Realistic
If the mold comes from the building, for example bad insulation, a leak or defective windows, and your landlord doesn't fix it within the deadline, you may be entitled to pay less rent until it's fixed. There's no fixed table, but court decisions give an idea:
| Situation (court examples) | Reduction |
|---|---|
| Mold in the bathroom | around 10% |
| Mold in a bedroom | around 15% |
| Mold on outside walls due to defective windows | around 20% |
| Mold in the living room | up to 50% |
| Mold in every room / serious health risk | 75–100% |
Who has to prove what? You need to prove the mold exists. If your landlord says it's your fault, he generally has to show the cause isn't the building, often with an expert's report. That's why your photos, written notice and humidity log are so valuable.
Does Insurance Help?
Your private liability insurance (Haftpflichtversicherung) can cover damage you cause to the rented flat (Mietsachschäden), like a burst pipe you caused. But be honest with yourself: mold that develops slowly from not airing is usually excluded in most policies. Insurance is a safety net, not a replacement for good habits. Still, every tenant in Germany should have it. Compare Haftpflichtversicherung tariffs via Tarifcheck →
More on why it's so cheap and so important in our Haftpflichtversicherung guide.
Moving Out? Protect Your Deposit
Mold is one of the most common reasons landlords keep part of the Kaution. Before your handover appointment (Wohnungsübergabe), check every corner, and if there was mold that the landlord knew about and was responsible for, bring your written correspondence. Never repaint over mold just before moving out. It comes back, and it looks like you tried to hide it.
Our Take
Lüften feels strange at first: opening the window wide when it's -2 °C outside sounds like burning money. But two weeks into the habit, it becomes automatic, your flat smells fresher, your heating bill doesn't explode, and you avoid one of the most stressful fights a tenant can have in Germany. Buy a hygrometer, air in the morning and after showers, keep furniture off the walls, and report problems in writing straight away.
Already dealing with mold or a landlord who won't respond? Share your situation in our Facebook group (without personal details). Many members have been through exactly this.
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