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How to Prevent Condensation on Windows

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How to Prevent Condensation on Windows

By Ruth MacEachern

Product Manager

Sep 15, 2021

As the weather starts to get cooler, the sight of condensation forming on bedroom windows when we wake up each morning becomes a common occurrence.  Most of the moisture that causes condensation on windows comes from breathing and is more common in autumn and winter because during those seasons we are more likely to sleep with our bedroom windows closed, so it is harder for the moist air to escape during the night.

What causes condensation

At a given temperature, air is able to hold a certain amount of moisture.  At room temperature – about 20 degrees Celsius, air can hold up to a maximum of 15 grams of water for every kilogram of air.  Air weighs about 1.2Kg per cubic metre, so in a room which is 3m x 4m x 2m, the air can hold a maximum of 540g of water – about half a litre.

When that warm air comes into contact with a cool surface such as a window, it cools and can hold less water.  Air at 15 degrees Celsius can only hold about ten grams of water per kilogram.  The moisture that was held in the air is released onto the cool surface, where it becomes condensation. 

When sleeping, a person can breathe out about forty grams of water per hour.  Overnight, two people sleeping in a room will breathe out about 640 grams of water in total – this is more than the air can hold and is what makes up the majority of condensation.

What are the risks of condensation on windows

On the windows themselves, condensation isn’t much of a problem, as it simply sits on the surface and does not soak in.  However, windows are not the only place in a room where condensation will form.  Cool exterior walls will also become moist, and it is on walls and other surfaces, where moisture can soak into the material itself that condensation can lead to damp problems including crumbling plaster, peeling wallpaper and even mould growth.

How to reduce condensation on windows

There are a number of ways to reduce the amount of condensation that can form in on windows overnight.  One simple tip is to avoid drying towels or wet clothing on bedroom radiators as this minimises the amount of excess moisture that is created in the room.

How to prevent condensation on windows

Improved airflow is the most effective way of preventing condensation forming on windows altogether.  Condensation will only form when moisture levels in the air exceed the capacity of the air to hold that moisture.  With better ventilation, air is moved out of the room before it has the chance to become saturated, and this prevents condensation altogether.

The best solution for improved airflow in bedrooms is a whole house ventilation system such as Positive Input Ventilation.  These systems have a centrally located hub which draws fresh, dry air into the house from outside and then distribute it gently into the home.  The advantage of a PIV system is that it operates very quietly and uses very little energy, so it will not disturb your sleep.

Find out more

If you are waking up to find condensation on your windows and want to prevent this becoming a bigger damp or mould problem, speak to one of our local ventilation specialists.  Book a free home survey today to get advice about the best system for your needs.

Need help with condensation, mould or damp problems?

One of our local experts will contact you to learn more about your problems, offer free expert advice and make recommendations for a permanent solution.

During the free survey we will

  • check Assess any condensation, damp or mould problems in your property
  • check Take readings of the relative humidity levels
  • check Identify any underlying problems and make recommendations for a permanent solution

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