How to stop condensation on windows in winter (UK guide)

Updated 26 October 2026 · Prices worked out at UK electricity rates

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Waking up to streaming windows is normal in a lot of British homes from October to March. It is not just annoying: the water soaks into window seals, sills and curtains, and that is where black mould starts. Here is how to stop it, starting with the free fixes.

Short answer: reduce the moisture you make (lids on pans, extractor fans, no unvented drying of clothes), let a little air through (trickle vents open, a window on the latch for 10 to 15 minutes in the morning) and keep rooms at a steady low heat rather than very cold. If windows are still wet every day, a dehumidifier in that room usually solves it.

Why it happens

Warm air holds more water than cold air. When the warm, moist air in your room touches cold glass, it cools and the water comes out as droplets. Bedrooms are the worst because two people breathing overnight release a surprising amount of moisture into a closed room, and the window is the coldest surface.

Free fixes, in order of impact

Open trickle vents (the small slots at the top of many uPVC windows) and leave them open all winter. The heat loss is small; the damp reduction is big.
Air the bedroom in the morning: open the window wide for 10 to 15 minutes, door closed. A short burst swaps damp air for dry air without chilling the walls.
Wipe the glass first thing with a squeegee or a microfibre cloth and wring it into the sink, so the water doesn't soak into the frame.
Use extractor fans while cooking and showering, and for 15 minutes after.
Dry clothes in one room with the door shut and the window cracked, not across radiators in the living room.
Keep furniture a few centimetres off outside walls so air can move behind it.
Avoid big swings in temperature. A room that drops very cold overnight gets more condensation than one kept at a steady, modest temperature.

When to get a dehumidifier

If you have done the above and the windows are still wet most mornings, the air in the room is simply too humid. A dehumidifier running overnight, set to around 50 to 55% humidity, normally stops window condensation within a few days. For a cold bedroom a desiccant model usually works best. Read which type to choose.

Where to buy (prices change often, so check the current price):

Do window vacs and moisture traps help?

A window vac makes the morning wipe quicker and gets the water off without a soggy cloth. It treats the symptom, not the cause, but it is cheap and does stop water reaching the sills. Disposable moisture trap tubs collect a small amount of water. They can help in a wardrobe or a small cupboard, but they are far too small to dry a whole room.

When it is more than condensation

If walls are damp low down near the floor, there is a tide mark, or the patch is there in summer too, it may be rising or penetrating damp from a leak, gutter or damaged render. That needs a repair, not a gadget. If you rent, tell your landlord in writing: damp and mould are their responsibility to investigate.