Condensation on windows happens when warm, moist indoor air touches glass that is colder than the air’s dew point, and the water vapour turns back into droplets. To stop condensation on windows you need to do two things: put less moisture into the air, and get rid of the moisture you do produce before it finds the coldest surface in the room. Warmer glass helps too. Below we go through why it happens, the fixes in order of how much difference they make, and the signs that wet windows are telling you about something bigger.
Why do my windows get condensation?
Air always holds some water vapour, and warm air can hold more than cold air. Cool any parcel of air far enough and it reaches its dew point, the temperature at which it can’t hold all its moisture and some condenses out as liquid water.
On a cold morning the glass is usually the coldest surface in the room. Air next to it cools, hits its dew point, and leaves water on the pane. That’s why condensation is worst:
- first thing in the morning, after a night of breathing in a closed bedroom with the heating off;
- in kitchens and bathrooms, where cooking and showers put a lot of moisture into the air in a short time;
- in cold snaps, when the glass is at its coldest;
- on single glazing and older double glazing, which run much colder on the inside face than modern units.
The moisture comes from ordinary living. Cooking, showering, kettles, breathing and drying washing indoors all add to it, and the Energy Saving Trust puts a typical household’s output at up to 100 litres of moisture a week. None of that is a defect. Condensation is the normal result of a lot of moisture meeting a cold surface.
Single glazing, double glazing and condensation between the panes
Where the condensation sits tells you a lot:
| Where you see it | What it usually means | What to do |
|---|---|---|
| Inside face of the glass | Moist room air meeting cold glass | Reduce moisture, ventilate, keep rooms evenly warm |
| Between the two panes of a double-glazed unit | The unit’s seal has failed and moist air has got into the gap | Replace the sealed unit (the glass), not usually the whole window |
| Outside face of the glass | The glass is well insulated, so the outer pane stays cold | Nothing. It clears as the day warms up |
Condensation between the panes is the one people most often get wrong. A double-glazed unit is two sheets of glass sealed around a dry, gas-filled gap. When the edge seal fails, damp air gets in and the unit mists up from the inside, and you can’t wipe it away. The Energy Saving Trust notes that you can usually replace just the glazed unit rather than the whole window. It’s a window fault rather than a damp problem, but the unit now insulates less well.
Single glazing, which is still common in the Victorian stone terraces and conservation areas of West Yorkshire and the Pennine towns, runs cold and will almost always collect some condensation in winter. That doesn’t mean old sash windows have to go. Secondary glazing, draught-proofing and good ventilation can make a big difference, and Historic England publishes guidance on secondary glazing for traditional windows.
How to stop condensation on windows: fixes ranked by effectiveness
Here is roughly what helps most, from the biggest gains down. Most homes need a combination.
1. Cut moisture at source
This is the cheapest fix and makes the biggest difference.
- Dry washing outside, or in a vented or condensing tumble dryer. A rack of wet clothes on a radiator puts litres of water into the room.
- Put lids on pans and keep the kitchen door shut while cooking.
- Keep the bathroom door shut during and after a bath or shower.
- Avoid portable paraffin or bottled-gas heaters. They have no flue, so the water vapour they make as they burn goes straight into the room.
2. Extract fans that actually work
A working extractor in the kitchen and bathroom removes moisture at the point it’s produced, before it spreads through the house. Check yours genuinely pulls air: hold a sheet of toilet paper against the grille and it should stick. The Energy Saving Trust suggests running fans for at least 15 minutes after a shower or bath, and using the cooker hood while cooking and for about 15 minutes afterwards. A fan that’s clogged, ducted badly or switched off at the isolator does nothing. Our guide to mould in the bathroom covers extract rates in more detail.
3. Trickle vents and short bursts of window opening
Trickle vents, the small slotted vents on the head of most modern window frames, give a constant low level of background ventilation. Keep them open and clear, especially in bedrooms. Many people shut them in winter and then find their bedroom windows streaming every morning.
Opening windows for a few minutes several times a day, particularly after cooking, showering and first thing in the morning, swaps moist air for drier outside air without losing much heat from the walls and furniture.
4. Steadier heating
Cold rooms and cold surfaces attract condensation. Low, steady background heat keeps glass, walls and window reveals above the dew point more of the time than short, intense bursts of heating with the house cold in between. Unheated spare bedrooms are classic condensation traps, especially when moist air from the rest of the house drifts into them.
5. A dehumidifier
A dehumidifier is a useful tool where you can’t easily ventilate, for example a basement flat, a room where washing has to be dried indoors, or a cold spell. It treats the symptom rather than the source, but it treats it well. Empty it regularly. Small moisture-absorbing pots on the windowsill help very little by comparison.
6. Window upgrades
Better glazing raises the inside temperature of the glass, so condensation forms less readily. The Energy Saving Trust notes that more efficient glazing reduces condensation. But new windows are the most expensive option on this list, and they can move the problem rather than solve it. A modern, well-sealed window cuts down the accidental ventilation the house used to get, and the moisture then condenses on the next coldest surface, often a wall corner or a window reveal, where it feeds black mould. If you replace windows, make sure the new frames have trickle vents and that the kitchen and bathroom extraction works.
Should I wipe condensation off the windows?
Yes. Wiping windows and sills each morning stops water soaking into timber frames, sills and the plaster around the window, which is where rot and mould start. Wring the cloth into the sink rather than drying it on a radiator, or you’ve just put the water back into the air. A window vacuum makes the job quicker.
When condensation on windows signals a bigger problem
Some condensation on cold winter mornings is normal. These signs suggest something more:
- Mould on the window reveals, ceilings or wall corners as well as on the glass. The whole room is too humid for too long, or there’s a cold spot such as a cold bridge (a lintel or concrete beam carrying cold through the wall) or missing insulation.
- Rotten timber sills or frames, or water running off the sill and staining the wall below.
- A musty smell and damp-feeling soft furnishings, which point to persistently high humidity.
- Damp patches that don’t follow the pattern of condensation. A patch that appears after heavy rain, or a tide mark low on the wall, is a different kind of damp entirely. Our guide to telling rising damp, condensation and penetrating damp apart explains the differences.
- Condensation that started after building work. New windows, a blocked-up fireplace, sealed-up air bricks, or cavity wall insulation installed in the wrong wall can all change how a house handles moisture.
If you’re not sure which you’re dealing with, our free damp checker asks a few questions about what you’re seeing and points you towards the likely cause.
Condensation in rented homes: landlords and tenants
Condensation is often treated as a “lifestyle” problem that tenants cause and must solve. Government guidance on damp and mould in rented housing rejects that. Landlords are expected to take reports seriously, find the underlying cause and fix it, not blame the occupants. For social housing, Awaab’s Law has been in force since 27 October 2025 and sets legal timescales for landlords to investigate and make safe damp and mould hazards that pose a significant risk to health.
In practice, a home that only stays dry if the tenant lives with the windows open and the heating on all day has a building problem. Common culprits are no working extraction, no trickle vents, poor insulation, cold bridging, or window and wall defects. Landlords who want to get ahead of a complaint, or tenants and landlords who disagree about the cause, benefit from an independent assessment that looks at the building and the way it’s being used, and says plainly which is which.
If you’re buying
Heavy condensation and mould around windows on a viewing tell you how the house behaves. Fresh paint on the window reveals can hide it. A Home Survey Level 2 will note signs of condensation and dampness, and where there’s a specific worry an independent damp and timber survey will find the cause and recommend proportionate fixes. We sell no windows, fans or damp treatments, so our advice is only about what the building needs. Get in touch with the address and what you’re seeing.
Sources and further reading
- How to get rid of damp — Energy Saving Trust
- Energy efficient windows and doors — Energy Saving Trust
- Damp and mould: understanding and addressing the health risks for rented housing providers — GOV.UK
- Awaab’s Law to force landlords to fix dangerous homes — GOV.UK
- Energy efficiency and historic buildings: secondary glazing for windows — Historic England