It's winter here, which means that in our old house the windows get condensation forming on the inside overnight in the rooms where people sleep. Sometimes there is so much that it streams down and makes puddles on the windowsill.

Is there any way to stop this happening? I can't put things on the windowsill at the moment as they'd get ruined by the water.

  • Don't you air your rooms? It gets down to -15C here every winter, but we always have the window "tipped" when we sleep. People lose a lot of water while sleeping, you need to get it out of there. – RedSonja Mar 12 '15 at 14:06

Condensation is formed when warm air meets the cold glass and the water vapour in the air condenses into water droplets.

There are a few ways you can mitigate this:

  • Warm the glass. This is extremely energy-inefficient (with the associated expense and detriment to the environment that that implies), but warming the glass by pointing a fan heater at it or installing a radiator beneath it and turning the heat up high would reduce the effect of cold air hitting the window.

  • Install thicker curtains. This better insulates the warm room-air from reaching the cold glass in the first place (not to mention keeping your room warmer) which will reduce the effect of condensation.

  • Make the room colder. Instead of using radiators and heaters to warm the entire room, use hot water bottles and blankets to warm only the space that you sleep in. There will be less of a temperature difference between inside and outside, resulting in less condensation on the windows.

  • Buy a dehumidifier. By taking the water vapour out of the air, there will be less water to condense on the glass. Following on from this, use extraction fans when boiling water on the stove or running a bath or shower (or keep the kitchen/bathroom doors shut) to prevent humid air from escaping to the rest of the house.

  • A lifehack-y version of the dehumidifier option would be to keep a large jar of silica gel or other dehumidifying chemical (talc?) near to the window. I'm not sure how effective this would be without cycling the air; my suspicion would be that the warm humid air would rise above the silica gel unless you put it really high up. However, I included it so that you can experiment if you so desire.

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