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Condensation: why it happens and how to stop it
Streaming windows in the morning, damp window sills, black mould in the corners — that's condensation, the most common form of damp in UK homes. The good news: it's also the easiest to deal with once you understand it.
What causes condensation
Everyday living puts a surprising amount of water into the air — cooking, showers, drying clothes indoors and even breathing. Warm air holds that moisture; when it touches a cold surface (a window, a cold external wall, an unheated room) it cools and releases the water as condensation. That's why it's worst in winter, overnight, and in the coldest corners.
Condensation on windows
Misted or streaming windows are the classic sign. Condensation on the inside of the glass means too much moisture in the room air. (Condensation between double-glazing panes is different — that means the sealed unit has failed and needs replacing.) Wiping the glass helps for an hour; reducing the room's humidity fixes it.
How to stop condensation
Three levers, used together:
- Ventilate — extractor fans on when cooking or showering, lids on pans, trickle vents open, and avoid drying washing on radiators.
- Heat evenly — a little background warmth keeps surfaces above the temperature at which air condenses.
- Dehumidify — take the moisture straight out of the air. A dehumidifier with a humidistat runs only when needed and is the quickest way to stop condensation and the mould it causes.
When to use a dehumidifier
Reach for one when ventilation and heating alone aren't keeping up — for example a flat that can't be aired easily, a bedroom with streaming windows, or a home where washing has to be dried indoors. It's also the fastest way to dry a room out after a damp spell. Hiring is ideal for a short-term problem: find your town for a local quote.
Frequently asked questions
Why is my window wet in the morning?
Overnight the room cools, the glass gets cold, and moisture in the air condenses on it. It signals high humidity in the room — ventilation, heating and a dehumidifier will fix it.
Does opening windows help?
Yes — ventilation lets moist air out, especially after cooking or showering. But in cold, wet weather it isn't always enough on its own, which is where a dehumidifier comes in.
Will a dehumidifier stop condensation?
Yes. By holding the room's humidity down it stops moisture condensing on cold surfaces, which also prevents the black mould condensation causes.