Why Window Condensation Happens in Winter
Condensation on windows — the familiar fogging or water droplets on the inside of glass — is especially common in winter. It occurs when warm, moist indoor air meets a cold window surface. Because the air cools down rapidly at the glass, its capacity to hold water vapour drops, and the excess moisture condenses into droplets.
Several household factors worsen the problem: cooking, showering, drying clothes indoors or simply breathing in a closed room all add moisture to the air. Also, modern homes with good sealing (which prevent drafts) often trap humid air inside — but if windows are poorly insulated (e.g. single-pane), the glass remains cold, encouraging condensation.
In short: high indoor humidity + cold window surfaces + poor ventilation = condensation.
Why It’s Worth Preventing
Left unchecked, condensation doesn’t just fog up your windows. Persistent moisture can damage wooden window frames and sills, rot paint or plaster, and encourage mould or mildew — which may affect building integrity and indoor air quality.
Moreover, condensation signals that your home isn’t optimally insulated or ventilated — which often means heat loss and higher energy bills in winter.
So, preventing condensation improves comfort, preserves your home, and can even save energy.
Effective Steps to Stop/Reduce Condensation
Here are practical, tried-and-tested ways to reduce condensation during a winter season:
1. Control indoor humidity
- Use a dehumidifier in rooms prone to dampness (bedrooms, bathrooms, kitchens) to keep humidity in check. Experts recommend aiming for 30–50% relative humidity.
- Avoid drying clothes indoors, particularly in poorly ventilated rooms. Wet laundry releases a lot of moisture.
- Cover pots while cooking, or use lids when boiling water — cooking steam greatly increases indoor humidity.
2. Improve ventilation
- Use exhaust fans in kitchens and bathrooms to expel humid air outside, especially when cooking, showering or using hot water.
- Open windows (or doors) briefly every day, even in winter — a 10–15 minute “airing out” helps exchange moist air with drier outside air.
- Keep internal doors open to ensure airflow throughout the home — don’t let moisture get trapped in a single room.
3. Improve insulation and window quality
- Upgrade windows: If your windows are old or single-glazed, consider upgrading to double glazing — these keep the interior glass surface warmer and reduce condensation.
- Seal gaps around windows: Use weather-stripping or sealant to stop cold drafts from making the window surfaces chillier.
- Use insulating curtains, blinds or thermal window films to add a barrier between cold glass and warm indoor air — especially useful overnight or in very cold weather.
4. Maintain a stable, moderate indoor temperature
Large temperature swings — e.g. heating up during the day, then turning the heat off at night — create cold spots that encourage condensation. A stable temperature helps reduce moisture deposition.
If possible, position radiators under windows (common in many homes). The rising warm air helps keep window surfaces warmer and discourages condensation.
Summary
Condensation in winter is nothing more than physics: warm, moist indoor air condensing on cold windows. But the effects — dampness, mould, wasted energy — can be significant. By controlling indoor humidity, improving ventilation, upgrading window insulation, and maintaining a steady temperature, you can dramatically reduce or even eliminate condensation.
If you incorporate these habits — ventilating during/after cooking or showering, drying clothes outside or in ventilated spaces, and using dehumidifiers — over the long term you’ll likely stop condensation from becoming a recurring winter headache.
Explore our range of double glazed windows and speak to our experts to know more.
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