How to Prevent Condensation in Winter

Winter condensation is worse because windows are colder and homes are sealed tight. Here's how to manage it.

Why Is Condensation Worse in Winter?

Two reasons: colder windows and sealed homes. In winter, outside temperatures drop, making window glass much colder. Even with double glazing, the inner pane can drop to 10-15°C on cold nights. When warm indoor air (typically 18-21°C) contacts this cold glass, moisture condenses.¹

Homes are also more sealed in winter. Windows stay closed, trickle vents are often shut to save heat, and extractor fans are used less. This traps moisture from cooking, showers, and breathing, raising indoor humidity.

Heating Patterns

Keep heating consistent rather than cycling on/off. A house that cools overnight and reheats in the morning experiences more condensation because cold surfaces accumulate moisture when heating is off, then dry slowly when heating comes back on.

Aim for 18-21°C in living areas and 16-18°C in bedrooms. Lower temperatures save energy but increase condensation risk because surfaces are colder. If you see persistent condensation, raise the thermostat by 1-2°C and see if it improves.²

Avoid heating one room heavily and leaving others cold. Cold rooms (especially north-facing bedrooms and unheated spare rooms) are condensation hotspots because surfaces stay below the dew point.

Ventilation in Winter

Keep trickle vents open even though it feels counterintuitive. Closing them saves a small amount of heat but traps moisture, raising condensation and mould risk. Trickle vents provide 8,000 mm² background ventilation (the Part F minimum) without creating draughts.

Use extractor fans in kitchen and bathroom during and for 15-20 minutes after use. In winter, people often turn fans off quickly to save heat. This leaves moisture in the air, which then condenses on windows and walls.

Open windows briefly (10-15 minutes) in the morning to purge overnight moisture, especially in bedrooms where occupants have been breathing and releasing moisture for 8 hours. This is more effective than leaving windows ajar all day.

Reduce Moisture Sources

• Dry clothes outside or in a vented tumble dryer. Drying clothes on radiators indoors releases 2-3 litres of water into the air.
• Lid pans when cooking to trap steam. Use the extractor hood or fan.
• Shower with the door closed and extractor fan running. Leave the fan running for 15-20 minutes after.
• Don't overfill kettles. Boiling more water than needed releases excess steam.
• Limit indoor plants in winter, especially in bedrooms. Soil and transpiration release moisture.

Monitor Indoor Humidity

Use a hygrometer (costs £10-£20) to track indoor relative humidity. Aim for 40-60% RH. Above 60%, condensation risk rises. Above 70%, mould risk is high.³

If humidity stays above 60% despite ventilation, you may need mechanical ventilation (MVHR or continuous extract fans) to remove moisture more effectively.

Minimum Room Temperature

18°C (living areas), 16°C (bedrooms)

Target Indoor Humidity

40-60% RH (year-round)

Extractor Fan Runtime

15-20 minutes after cooking/showering

Morning Window Purge

10-15 minutes (bedrooms especially)

Last reviewed: 20 May 2026 | Word count: 598 | Reading time: 3 minutes