How to stop condensation on windows in winter

10 minutes a day. Costs nothing to a few dollars.

Try this first (costs nothing): wipe the glass and sill with a dry cloth every morning, then open a window for five minutes. Condensation is water vapour from cooking, showers, breathing and drying clothes landing on cold glass.

What lowers the damp

• Run the extractor fan or open a window when you cook and shower. Close the bathroom door.
• Dry washing outside or in a room with a window open.
• Keep the heating steady. Cold rooms get more condensation.
• Leave space between furniture and outside walls so air can move.
• Lids on pans when cooking.

If that does not work

A small dehumidifier or moisture absorber may help in a damp room. A cheap hygrometer shows indoor humidity. Many sources give a range of around 40 to 60 percent as comfortable, but ask a professional for your home.

Black mould, damp patches that grow, or musty smells point to a bigger problem, such as a leak or poor ventilation. If you rent, tell your landlord in writing. If you own, ask a damp or building surveyor. Mould can affect some people's breathing, so ask a doctor if anyone is unwell.

Skip it if

Skip sealing vents to keep heat in. They let damp air out. For other damp-related smells, see washing machine smell fix.

Worked example

Take a bedroom with wet windows each morning. Round numbers: two people breathing overnight put a fair amount of water into the air. Open the window a crack at night, or open it wide for five minutes when you wake. Wipe the glass, then shut it. Many people notice the glass is drier within a few days. If the window is still streaming after a week, move the washing out of that room and check the fan.

Common mistakes

• Drying clothes on a radiator in a shut room. It adds a lot of water to the air.
• Turning heating off completely. Cold walls and glass collect water.
• Ignoring black spots. Mould on window frames starts small.
• Blocking trickle vents. They are there for airflow.

Black spots on bath sealant are covered in how to remove mould from bathroom sealant.