Condensation running down your windows on a cold London morning is more than a nuisance. If it is left to sit, it can damage paintwork, cause mould and make rooms feel damp and chilly.
What causes condensation on windows in winter?
Condensation appears when warm, moist indoor air hits cold glass and cools rapidly. The water vapour in the air turns into tiny droplets on the surface, just like steam on a bathroom mirror.
In winter, this is much worse because the outside temperature is low and your heating is usually on. That temperature difference makes the inner surface of the glass colder, so moisture is far more likely to settle there.
Modern homes are also better sealed, which is good for energy bills but traps moisture indoors. Everyday activities such as cooking, showering and drying clothes all add water vapour to the air.
Condensation on the surface vs between the panes
Before you try to fix the problem, it helps to know what kind of condensation you have. Surface condensation is on the room-side of the glass and you can wipe it away with a cloth. This is usually a ventilation, heating or moisture issue.
If you see misting or water droplets between the panes of double glazing that you cannot reach to wipe off, the sealed unit has likely failed. In that case, the window is no longer airtight and needs professional attention rather than dehumidifiers and trickle vents.
Quick troubleshooting checks
Is the moisture on the room-side and wipes off easily? Focus on ventilation, heating and cutting moisture sources.
Is the mist trapped between panes? Read a guide such as a dedicated condensation inside double glazing post and speak to a glazier about sealed-unit replacement.
Is mould starting on frames or walls? You will need to tackle both the moisture problem and safe mould removal.
Improving ventilation without freezing the house
Good ventilation lets moist air escape, so it is less likely to condense on your windows. In winter, it is about controlled airflow rather than leaving windows wide open all day.
First, check that bathroom and kitchen extractor fans are working properly and used every time you cook or shower. Run them for at least 15 minutes after you finish to clear excess steam, and clean the covers regularly so they can pull enough air.
Next, look at your window trickle vents. These are the small vents at the top of many modern windows. Keep them open during the heating season so a steady flow of fresh air can dilute humid indoor air without big draughts.
If you do not have trickle vents, consider short “airing” sessions. Open windows opposite each other for 5 to 10 minutes to create a cross-breeze, ideally after cooking or showers when moisture levels peak.
Managing moisture sources in everyday life
Reducing the amount of moisture you create indoors is just as important as getting rid of it. Small daily habits make a big difference to how wet your windows get overnight.
Try to avoid drying laundry on radiators in living spaces, especially bedrooms. If you must dry clothes indoors, use a clothes airer in one room with the window slightly open and the door closed to contain the moisture.
When you cook, put lids on pans and use the extractor on a high setting. In bathrooms, keep doors closed while showering and open the window or run the fan afterwards to let the steam out rather than into the rest of the house.
Heating, dehumidifiers and steady room conditions
A home that constantly swings between very warm and quite cold will have more condensation problems. Trying to heat up a very cold room quickly sends warm, moist air straight to chilled glass where it condenses.
Instead, aim for steady background heating in the rooms you use most, especially bedrooms. Keeping the glass slightly warmer reduces how much water will settle on it. Even turning radiators down a little but leaving them on for longer can help.
Dehumidifiers can be very effective in damp-prone homes or older London properties. Place them in the worst-affected rooms, away from walls and furniture, and close windows and doors so they can pull moisture from the air efficiently.
Empty the water tank often and check the manufacturer’s recommended room size. A small unit in a large open-plan space will not keep up, so you may need a more powerful model or to focus on one room at a time.
Checking vents, trickle vents and air bricks
Blocked or painted-over vents are a common cause of stubborn condensation. Outside, check air bricks and wall vents are not obstructed by soil, plants or stored items. These allow the building to breathe and help moisture escape.
Inside, look for furniture pushed tightly against external walls and under windows. Leaving a small gap behind large wardrobes or sofas helps air to circulate and reduces cold, damp patches where mould can take hold.
Dealing with mould safely
Persistent condensation often leads to black mould on window frames, sills and surrounding plaster. Mould spores can affect indoor air quality, so it is important to deal with it carefully.
Wear gloves and, if possible, a basic mask when cleaning mould, and avoid dry brushing which can spread spores into the air. Use a mould-specific cleaner or a diluted household bleach solution on non-porous surfaces, following the safety instructions.
If mould covers a large area, keeps returning quickly or affects vulnerable people such as young children, older adults or those with breathing issues, speak to a professional. They can assess moisture sources and advise on safe treatment.
When condensation points to glazing problems
Sometimes, ongoing condensation can indicate issues with the windows themselves. Cold draughts around the edges, or water collecting in the frame, can mean failed seals or damaged gaskets that leave the glass colder than it should be.
If you see misting between panes, notice that rooms feel draughty near closed windows, or the rubber seals look cracked and perished, it is worth asking a local glazier to inspect them. In many cases, only the sealed unit needs replacing, not the entire window frame.
You can also check for whistling noises in windy weather or movement in the glass when you gently press on it. These are signs that the unit is not properly sealed, which affects both condensation and heat loss.
Next steps if your condensation problem will not improve
If you have improved ventilation, reduced moisture, kept heating steady and perhaps added a dehumidifier but your windows are still running with water every winter morning, it may be time for a professional assessment.
For London homes, a glazing specialist can check for failed seals, poor fit, cold bridging around frames and advise if repair or sealed-unit replacement is the best option. They can also help you decide whether trickle vents or other upgrades would be useful.
If persistent window condensation or suspected seal failure is a concern in your property, contact Hunters Glass Ltd on 03301331655 to book an inspection. Visit the domestic glazing page for more information.
