How to stop condensation on windows

Why windows get wet

Every room has a dew point, the temperature at which its air would start to condense. It depends on the air temperature and relative humidity. At 20 °C and 60 % RH the dew point is about 12 °C, so any surface colder than that collects water. On a cold night the inside of a window can easily be below that. Try your own numbers with the dew point calculator, and see dew point explained.

Bedrooms are often worst because people breathe out moisture overnight with the door shut, and the room cools once the heating goes off.

Reduce moisture at the source

These habits cost little or nothing and tackle the problem where it starts. Drying washing indoors is one of the biggest sources; see how to dry clothes indoors quickly.

• Put lids on pans and use the cooker hood when cooking
• Run the bathroom extractor during and after showers, door shut
• Dry washing in one room with a dehumidifier, or outside when you can
• Vent tumble dryers outside, or use a condenser or heat pump model
• Avoid paraffin or bottled gas heaters, which add moisture

Ventilate sensibly

Open trickle vents at the top of window frames and leave them open; they are designed to let a small, steady flow of air through. Opening a window a little for a short time after cooking or showering lets moist air out. In bedrooms, leaving the door ajar or a trickle vent open overnight helps.

Ventilation lets heat out too, so the aim is little and often rather than windows wide open all day.

Keep surfaces warmer

A steady, low level of heating keeps the glass and walls above the dew point better than blasting heat for an hour and then letting the room cool. Keep curtains and blinds from trapping cold air against the glass overnight where you can, or open them first thing. Double or secondary glazing keeps the inner pane warmer, which is why it condenses less.

Furniture pushed against cold outside walls creates cold spots too. Leave a small gap behind wardrobes and beds.

Use a dehumidifier

If habits and ventilation are not enough, a dehumidifier lowers the moisture in the air so the dew point drops below the temperature of the glass. Set it to around 50 % RH in a bedroom with condensation, close the door and let it run. A compressor model suits a heated room; a desiccant model suits a cold one and adds a little warmth.

Our humidity settings guide has targets by room, and our buying guide lists models suited to condensation.

Best dehumidifiers for condensation →

When it is more than condensation

If water appears in one spot regardless of the weather, is worse after rain, or comes with damp patches around the frame or on the wall below, there may be a leak, failed seals or another building problem. Blown double glazing, where the mist is between the panes, needs the sealed unit replaced. For persistent damp, speak to your landlord if you rent, or a qualified surveyor or glazier if you own. See how to treat damp walls.

Frequently asked questions

How do I stop condensation on windows overnight? Open trickle vents, keep the bedroom door ajar or run a dehumidifier at around 50 % RH, and keep a steady low heat rather than letting the room go cold.

Is condensation on windows normal? A little on cold mornings is common in UK homes. Heavy condensation every day means the air is too humid and needs ventilation or a dehumidifier.

Does a dehumidifier stop window condensation? It usually reduces it a great deal by lowering the room's humidity and dew point. Combine it with ventilation and steady heating.