How can you prevent condensation on windows?
How to prevent condensation on windows: where the moisture comes from, how to ventilate and heat properly, and when a dehumidifier helps reduce humidity.
Why condensation forms on windows
Condensation forms on the inside of windows because moisture from the warm room air condenses on the cold window pane.[1] When warm air cools down at windows, the relative humidity there rises.
Once it reaches 100 percent, condensation becomes visible on the smooth pane.[2]
The window pane is usually one of the coldest points of the building envelope, especially in older buildings and with older windows.[1] The colder the pane, the more water condenses. That is why condensation occurs mainly in winter.
The moisture is produced by everyday living: cooking, showering and breathing release around 1 to 2 litres of water per adult into the room air every day.[3] Overnight, this moisture collects in the closed bedroom, and in the morning the pane is wet.
Less humidity means dry panes
Less humidity in the room is the real lever against wet panes. The less water vapour the air contains, the later it reaches 100 percent at the cold pane. Only then does water settle. In winter, a good humidity level in the air is below 50 percent.[4]
High relative humidity can lead to condensation on windows and increase the risk of mould growth. An electric dehumidifier helps you lower the humidity.
Our Beurer LE 250 removes up to 20 litres of moisture from the room air per day, even in large rooms up to 60 m². It works preventively against mould, condensation and musty odours.
Our LE 250 steps in where ventilation reaches its limits. This refers to moisture that keeps building up in the room. With its automatic mode, it is suitable for continuous dehumidification and keeps the humidity between 45 % and 55 %.
Ventilating properly and heating evenly
Airing your home properly in winter means: short, strong bursts, several times a day. That sounds simple, and it is. Ventilate 4 to 5 times a day for 5 to 10 minutes with short bursts of fresh air so that the moisture can escape; otherwise mould can form.[3] The bathroom and kitchen are the biggest sources of moisture in the home. So ventilate immediately after showering or cooking.
Even heating is the second half of the solution.
Colder indoor air increases the risk of higher relative humidity and condensation on cool surfaces.[1] Keep indoor temperatures as constant as possible and keep unused rooms slightly heated, and keep doors between rooms at different temperatures closed.[5]
Furniture plays a role too. Place large pieces of furniture such as sofas or armchairs 5 to 10 cm away from exterior walls so the air can circulate, and don't block the radiators.[3]
| Cause | How you recognise it | What you do |
|---|---|---|
| Humidity from the bathroom and kitchen | Panes fog up after showering or cooking | ventilate with short bursts of fresh air immediately, close doors |
| Night-time humidity in the bedroom | The pane is wet in the morning | ventilate in the morning, measure the humidity |
| Cold, unused rooms | Condensation mainly in one room | keep the room slightly heated, close the door |
| Persistently high humidity | The hygrometer shows over 50 percent in winter | additionally use a dehumidifier |
Measuring humidity and lowering it with a dehumidifier
Measuring the humidity shows you whether your ventilating is enough. We recommend a thermo-hygrometer for this. Our Beurer HM 22 displays the temperature, relative humidity, date and time. After switching it on, the HM 22 can take 10 minutes to display the temperature and humidity correctly. How accurately different devices measure is covered in our hygrometer test guide.
In its test “Hygrometer-Test: Auf diese Modelle können Sie sich verlassen” (24.03.2026), the verdict of stern Kaufkosmos on the Beurer HM 22 reads (translated from German): “Narrowly beaten, but also reliable and recommendable without reservation is the Beurer HM 22, which has a timer on board as a small extra (for example for the kitchen).”[6]
If the hygrometer shows a persistent reading above 50 percent in winter despite ventilating, the Beurer LE 250 lowers the humidity in a targeted way. You set your desired humidity between 30 % and 80 % or use the automatic mode.
The night mode runs without disturbing lights or signal tones, and the timer can be set from 1 to 24 hours.
If you dry laundry in your home, the laundry drying mode of the Beurer LE 250 helps: it dehumidifies continuously at the highest fan level, so the moisture from the wet laundry does not spread through the room. Our removable 4-litre water tank is easy to empty; for continuous operation, you connect the supplied condensate hose.
Place the Beurer LE 250 with 50 cm of clearance on all sides. Only operate it in rooms with a floor area larger than 4 m².
Keep windows and doors closed while dehumidifying with the LE 250. Read the instructions for use before first use.
When condensation points to a bigger problem
Condensation that forms now and then is not an alarm signal. If it forms regularly, that is a sign of poor thermal condition of the building or of incorrect heating and ventilating. Wipe the water away regularly to prevent mould spreading from the silicone seals across the window.[5]
If the relative humidity stays above 60 percent for days and weeks, this can encourage mould growth within just a few days.[7]
If mould is already visible on the window, it is best to have professionals remove it, and the cause should be investigated.[1] A dehumidifier is no substitute for eliminating structural causes.
It helps to keep the humidity permanently low afterwards.
Airing is enough or a dehumidifier: your decision
Your hygrometer will tell you whether ventilating is enough. If, after ventilating with short bursts of fresh air in winter, the humidity drops back below 50 percent and the panes stay dry in the morning, ventilating and even heating are sufficient. Does it keep rising despite ventilating? Perhaps because laundry is drying indoors or a room has no window? Then a dehumidifier is the reliable solution.
The Beurer LE 250 dehumidifies enclosed indoor rooms and maintains 45 % to 55 % humidity in automatic mode. Wet rooms and unventilated cellars are excluded. Do not use it in the immediate vicinity of baths or showers., and maintains 45 % to 55 % humidity in automatic mode. Together with our HM 22, you can see at any time whether the humidity in the room is under control. You can find all our models under Beurer dehumidifiers.
Take a look at the Beurer LE 250 if your windows keep getting wet despite ventilating.
Frequently asked questions
Why are my windows wet despite ventilating?
Windows get wet despite ventilating when the room air quickly becomes humid again and the pane is very cold. Cooking, showering, breathing and drying laundry constantly add new moisture to the air. Measure the humidity; if it stays above 50 percent in winter, a dehumidifier like the Beurer LE 250 helps.
Why does condensation form on the window overnight?
Overnight, the moisture from breathing collects in the closed room while the pane cools down outside. At the cold pane, the air reaches 100 percent relative humidity and the water settles. Ventilate thoroughly in the morning and wipe the water away.
How can you prevent condensation?
You can prevent condensation by lowering the humidity and avoiding cold spots. Ventilate several times a day with short bursts of fresh air, heat evenly and keep a distance between furniture and exterior walls. If that is not enough, a dehumidifier like the Beurer LE 250 lowers the humidity permanently.
Is there a quick, cheap trick to stop condensation?
No single trick helps against condensation - what helps is less moisture in the room air. Wiping it away and ventilating vigorously with short bursts of fresh air work immediately. In the long term, it helps to measure the humidity with a thermo-hygrometer like the Beurer HM 22 and, if needed, to lower it with a dehumidifier.
