One cold October night is all it takes for the windows to be running with water by morning. Condensation on windows is the most visible warning that the air inside your home is carrying too much moisture. The good news is that it is almost always solved with habits, not building work.
Why condensation appears on windows
Warm air holds far more water vapour than cold air. When the room's mild, moisture-laden air touches the glass — the coldest surface in the room — it cools sharply and can no longer hold that vapour. The excess turns to liquid and runs down the pane. It is exactly what happens to a cold bottle straight out of the fridge.
Put another way: the window is not the cause, it is the thermometer. Single glazing only makes the problem more obvious, because it stays colder than double glazing. If the moisture isn't taken out of the air, it will condense somewhere else, usually behind a wardrobe pushed against an external wall, where you won't see it until the mould appears.
The moisture comes from inside (and there's more of it than you think)
A family of four easily releases between 10 and 15 litres of water a day inside the home. The main sources are:
- Breathing and perspiration: around 1 to 2 litres per person every 24 hours.
- Cooking: 2 to 3 litres a day, especially with uncovered pans.
- Showers: about half a litre each.
- Laundry dried indoors: 2 to 3 litres per wash load. It is the single biggest source.
All of that has to go somewhere. In a well-sealed home, with new windows and no ventilation, it doesn't.
How to get rid of condensation on windows: 6 fixes ranked by effectiveness
- Purge ventilation, every morning. Opening two opposite windows wide for 5 to 10 minutes replaces all the air without cooling the walls. It is far more effective, and cheaper, than leaving a window ajar all day.
- Never dry laundry indoors without ventilating. If an indoor airer is your only option, put it in a room with the window open and the door closed, or stand a dehumidifier next to it.
- Use the cooker hood and the bathroom extractor, and leave them running 15 minutes longer. The steam doesn't vanish when you turn off the tap: it carries on circulating through the house.
- Keep the temperature steady. A constant 18 or 19 ºC produces less condensation than heating hard in the evening and switching everything off afterwards. Cold walls always condense.
- Pull furniture away from external walls. Five centimetres is enough for air to circulate. That gap is where most mould starts.
- A dehumidifier, if relative humidity goes above 65%. The healthy range is 40 to 60%. A cheap hygrometer will tell you whether you really need one or whether better ventilation is enough.
What about the water already on the glass?
Wipe it off every morning, without fail. A small rubber squeegee clears it in seconds, and a microfibre cloth finishes the corners and the seals. It is in the rubber seal that black mould takes hold first, and once it does the staining is permanent. If you can already see dark spots, clean them with water and heavily diluted bleach and let them dry with the window open.
Not all damp is condensation
Before investing in a dehumidifier, confirm where it is coming from. Condensation appears in the morning, on cold surfaces, and fades over the course of the day. A leak leaves stains that grow when it rains and concentrate in one spot on the ceiling or the wall. Rising damp climbs up from the floor, to around a metre high, and lifts the paint. Those last two won't be fixed by ventilating: they need building work.
With a ten-minute daily routine, condensation on windows stops being a winter problem. Find more ideas for a more comfortable, practical home at the Velia Select store.