How to Stop Condensation on Windows UK

First, identify where the condensation is

Before changing your heating or ventilation, check which side of the glass is wet.
Condensation on the inside, outside or between the panes usually points to different causes and requires a different response.

If the condensation is on the room-facing side of the glass, the steps below will help you reduce the moisture and make the window surface less prone to condensation.

Why does condensation form on windows?

Air inside a home contains water vapour from normal activities such as breathing, cooking, showering and drying clothes. When humid indoor air touches a sufficiently cold surface, some of that vapour turns into liquid water. Windows are a common place to see this because glass is often colder than the surrounding walls.

Energy Saving Trust notes that regular condensation can be a sign that a home needs better ventilation, particularly when moisture is repeatedly building up faster than it can escape.

A small amount of condensation after a shower or on a bedroom window on a cold morning is not unusual. Persistent heavy condensation, water running down frames, recurring mould or damp smells need more attention.

Improve ventilation before sealing the room more tightly

Ventilation removes moisture and stale air in a controlled way. This is different from unwanted draughts. A room can be both draughty and badly ventilated if air is leaking in the wrong places while moisture is not being extracted where it is produced.

• Keep trickle vents open and unblocked, including in winter.
• Use bathroom extractor fans during and after showers or baths.
• Use kitchen extraction when cooking.
• Open windows for short periods to boost ventilation when needed.
• Keep internal airflow routes clear so moisture can reach extract points.
• Maintain and clean extractor fans so they continue to work effectively.

If you have recently draught-proofed doors or windows, check that you sealed only unwanted gaps rather than designed ventilation. See How to Draught-Proof Doors and Windows UK.

Reduce the amount of moisture entering the room

A typical household creates moisture every day through normal living. You do not need to eliminate all moisture; the aim is to stop it building up faster than the home can remove it.

Cooking

Use lids on pans where practical and use extraction while cooking. Moisture from boiling water can spread beyond the kitchen if it is not removed.

Showering and bathing

Use the extractor fan and, if practical, keep the bathroom door closed while producing large amounts of steam so moisture is extracted rather than distributed through the home.

Drying clothes indoors

Indoor laundry can add a substantial amount of moisture to the air. If you must dry clothes indoors, use a well-ventilated space and boost ventilation. A dehumidifier can assist with moisture removal, but it should not be treated as a substitute for ventilation. For a practical room-by-room setup, see How to Dry Clothes Indoors Without Damp or Mould UK.

Bedroom moisture overnight

Bedrooms can develop condensation by morning because occupants release moisture through breathing while the room and window surfaces cool overnight. Keep designed ventilation working and avoid sealing the room completely.

Keep cold surfaces from becoming unnecessarily cold

Condensation risk rises when moisture-laden air meets very cold surfaces. Keeping a room reasonably and consistently heated can help reduce the temperature difference between the air and the glass.

This does not mean overheating the room. The more efficient approach is usually to combine sensible heating with reduced heat loss and adequate ventilation.

For cold bedrooms, use How to Keep a Bedroom Warm Without Central Heating UK. For wider heat-loss checks, see How to Stop Heat Loss in a Room UK.

Will a dehumidifier stop window condensation?

A plug-in dehumidifier can lower indoor humidity by removing water from the existing air. In rooms that regularly stay humid, this can reduce the amount of moisture available to condense on cold glass.

However, Energy Saving Trust is clear that dehumidifiers do not provide fresh air. You still need ventilation for indoor air quality and to remove pollutants.

If humidity remains high despite sensible ventilation and moisture control, a dehumidifier may be worth considering. However, prioritise identifying and fixing the cause of persistent moisture rather than buying a device by default.

What if condensation has already caused mould?

Mould should be treated as a separate problem, not just wiped away while the moisture source continues. Energy Saving Trust advises dealing with mould promptly and improving ventilation at the same time.

When cleaning mould, follow the instructions on an appropriate mould-removal product. Avoid dry brushing, which can disturb spores. Ventilate the area and keep doors to other rooms closed while cleaning where practical.

When condensation may signal a building problem

Not every damp patch is condensation. Water can also enter through plumbing leaks, failed seals, roofs, gutters, walls or other defects. Rising damp and penetrating damp require a different diagnosis.

Investigate further if you see:

• a localised damp patch that remains wet regardless of cooking or showering
• staining that becomes worse after rain
• damaged plaster, skirting or flooring
• a persistent musty smell from one specific area
• water between double-glazed panes
• mould returning quickly despite improved ventilation and moisture control

Energy Saving Trust advises resolving the root cause of damp rather than assuming every moisture problem is caused by occupant behaviour.

What if you rent your home?

If you are renting and persistent condensation, damp or mould continues despite reasonable ventilation and normal use, report it to your landlord or managing agent and keep a record of the problem.

In England, government guidance for housing providers makes clear that condensation can have several causes, including inadequate ventilation, building deficiencies and inadequate heating. The correct response depends on the condition of the property, not simply on telling occupants to change their behaviour.

A practical order of action

• Confirm whether the moisture is inside the window, outside it or between the panes.
• Keep trickle vents and extract ventilation working.
• Reduce avoidable moisture from cooking, bathing and indoor laundry.
• Ventilate briefly and effectively rather than leaving the home sealed all day.
• Keep the room reasonably warm and reduce major heat-loss problems.
• Use a dehumidifier only as an additional moisture-control tool where appropriate.
• Investigate leaks or building defects if the pattern does not fit ordinary condensation.