--- title: "Why are my windows wet every morning? | Home Comfort Lab" description: "Morning condensation means warm, moist air is meeting cold glass. What causes it and how to stop it." url: https://homecomfortlab.co.uk/damp/why-are-my-windows-wet-every-morning/ --- # Why are my windows wet every morning? Morning condensation means warm, moist air is meeting cold glass. What causes it and how to stop it. By [Pete Harvey](https://homecomfortlab.co.uk/about/), editor. Updated 14 October 2026. This page links to Amazon. As an Amazon Associate I earn from qualifying purchases. [More about how this site is paid for](https://homecomfortlab.co.uk/affiliate-disclosure/). ![A bedroom at night with breath vapour drifting from a sleeper to a cold, streaming window with mould in the corner.](https://homecomfortlab.co.uk/images/scenes/why-are-my-windows-wet-every-morning.svg) > **The short answer** > > Overnight, the air in a closed bedroom picks up moisture from your breath. When that warm, moist air touches glass that has been chilled by the cold outside, it cools below its dew point and the water comes out as droplets. Less moisture in the air, or warmer glass, stops it. ## Why it happens at night Air can only hold so much water vapour, and how much depends on its temperature. Warm air holds more than cold air. The temperature at which a given batch of air can't hold its water any longer is its dew point. In a bedroom at night three things line up. The door and windows are shut, so the moisture from two people breathing for eight hours has nowhere to go. The heating is often off or low, so the room cools. And the glass is the coldest surface in the room, because only a pane or two separates it from the outside. The air touching the glass drops below its dew point first, and that is where the water collects. Single glazing, old double glazing that has lost its seal, and metal frames all run colder than modern glazing, so they get wetter. North-facing rooms that never get sun on the glass are usually the worst. ## Is it a problem? A light mist that clears by mid-morning is normal in a UK winter. It becomes a problem when: - water runs down and pools on the sill or soaks into wooden frames - black spots appear on the window seals or the rubber gaskets - the walls around the window, or in the corners of the room, feel cold and damp or start to darken - the room smells musty Those are signs that the room's humidity is high enough, for long enough, for mould to grow. Mould needs damp surfaces, and wet glass is usually the first one you see. [Mould risk checker](https://homecomfortlab.co.uk/tools/humidity-mould-risk-checker/): Put in your bedroom's temperature and humidity to see how close it is to the point where mould grows. ## How to stop it Work down this list. The first few cost nothing. 1. **Wipe the glass and sills every morning.** Use a cloth or a window vac and wring it out down the sink, not over the radiator. Water left on the frame soaks in or evaporates back into the room. 2. **Open the trickle vents** at the top of the window frame, if you have them, and leave them open all winter. If you don't, open the window a crack for 10 to 15 minutes after you get up. 3. **Keep the bedroom door open** at night if you can, so moisture spreads into the rest of the house instead of concentrating in one cold room. 4. **Don't dry washing in the bedroom.** A load of wet clothes releases far more water than a night's breathing. 5. **Keep the room from getting very cold.** A low, steady background heat keeps the glass and walls warmer than heating the room hard for an hour and then letting it drop. 6. **Pull curtains and blinds back from the glass** during the day, and don't trap them against the window at night. Air behind a closed curtain gets very cold and very damp. 7. **Run a dehumidifier** if the room still reads above 60% humidity once the steps above are in place. > **Worth knowing** > > A cheap hygrometer on the bedside table tells you whether the room is actually humid or whether the glass is just very cold. If the room reads 50% and the windows still stream, the glazing is the weak point. ## Tools that help You don't need to buy anything to start. These are the two products that make the daily routine quicker or deal with a room that stays damp. ### For clearing the glass each morning Kärcher WV 2 Plus N - **Type:** Cordless - **Tank:** 100ml - **Battery:** 35 minutes A window vac sucks the water off the glass into a tank, so it goes down the sink instead of into a cloth. This one is rated to run for 35 minutes on a charge. [View on Amazon](https://homecomfortlab.co.uk/go/wv-a/) [Manufacturer specs](https://www.karcher.com/gb/en/home-and-garden/products/wv-2-plus-n-p16336510) ### For a bedroom that stays damp MeacoDry ABC 10L - **Type:** Compressor - **Extraction:** 10 litres a day - **Power:** 198W - **Noise:** 36dB - **Tank:** 2.6 litres - **Cost per hour:** 5.2p * Laundry mode A small compressor dehumidifier suits a heated bedroom. This one draws 198W, among the lowest of the models we list, so it is cheap to run in the day with the door shut. Switch it off at night. [View on Amazon](https://homecomfortlab.co.uk/go/dh-comp-10a/) [Manufacturer specs](https://www.meaco.com/products/meaco-meacodry-dehumidifier-abc-range-10l) [Dehumidifier size calculator](https://homecomfortlab.co.uk/tools/dehumidifier-size-calculator/): Answer four questions about your home and get the dehumidifier size and type that suits it, with what it will cost to run. ## When the windows aren't the real problem If the walls themselves are wet, if there is a tide mark low on the wall, or if a damp patch grows after rain, the water may not be condensation at all. That points to rising or penetrating damp, which needs a repair rather than more ventilation. [How to tell the types of damp apart](https://homecomfortlab.co.uk/damp/condensation-vs-rising-damp-vs-penetrating-damp/). If you rent, read [what your landlord must fix](https://homecomfortlab.co.uk/damp/damp-in-rented-home-landlord/). ## Read next - [Humidity and mould risk checker](https://homecomfortlab.co.uk/tools/humidity-mould-risk-checker/) (Calculator) Enter your room temperature and humidity to see your mould risk and the temperature at which walls and windows start to get wet. - [Best window vac for condensation](https://homecomfortlab.co.uk/damp/best-window-vac/) (Buying guide) A window vac clears morning condensation off the glass and sill. What to look for and which models suit it. - [Black mould on window seals: how to remove it](https://homecomfortlab.co.uk/mould/black-mould-on-window-seals/) (How to) How to clean mould from silicone seals and rubber gaskets, and when the sealant needs replacing. - [Dehumidifier running costs: popular models compared](https://homecomfortlab.co.uk/damp/dehumidifier-running-costs/) (Running costs) What each popular dehumidifier costs per hour and per month at the current price cap, from its rated power. --- As an Amazon Associate I earn from qualifying purchases. Links to shops are marked, and earning from them never decides what we recommend. [How this site is paid for](https://homecomfortlab.co.uk/affiliate-disclosure/). Running costs use 26.32p per kWh for electricity and 7.97p per kWh for gas, the [Ofgem price cap, Direct Debit average for England, Scotland and Wales](https://ofgem.gov.uk/news/changes-energy-price-cap-between-1-october-and-31-december-2026) for 1 October to 31 December 2026.