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Why Does Condensation Form on Windows

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Why Does Condensation Form on Windows

By Ruth MacEachern

Product Manager

Sep 25, 2023

During the cooler months of the year, you are much more likely to wake up to see your windows covered in droplets of water – condensation – but did you know why condensation forms on your windows? 

Condensation on Bedroom Windows

For most people, a clear sign that winter is on the way is waking up to find that their bedroom windows are covered in droplets of water from condensation.  Cooler temperatures at night mean that the air cannot hold as much moisture. When the temperature drops, the air in your bedroom cools, with the coldest parts of the room being found by the windows.

When warm, humid air meets the cold glass surfaces of your windows, it cools quickly and releases the water vapour in the form of droplets that build up on the window.  Nighttime condensation forms slowly, but you can see the same effect by exhaling onto a piece of glass.

Where does nighttime condensation come from?

The most common sources of moisture in the air of your home are cooking and bathing.  Large quantities of steam are released by these activities, but most people don’t cook overnight, so where does the condensation on our bedroom windows come from?

While some of the moisture in the air is residual from daytime activities, the main source of condensation forming overnight is actually the occupants of the room breathing.  Over the course of a day, the average person breathes out about 14,000 litres of air, and suspended in this air is about 400ml of water vapour.  When you’re warmly wrapped up in your duvet at night, the amount of water vapour that you breathe out increases, and it is this moisture that contributes to the condensation that you see in the morning.

If you, like most people, sleep with your bedroom door closed, the air in your room does not circulate as much as it would during the day, and as a result, the water vapour becomes trapped and increases the humidity in the bedroom to the point where the air can no longer hold it.

Once the capacity of the air to hold moisture is exceeded, condensation starts to form.

Can condensation cause problems?

Condensation on your bedroom windows might be unsightly, but provided that you wipe it away before it can soak into any wooden frames, it is unlikely to do any damage, however condensation will form on any cool surface in your room, and might not be as obvious as on your windows, particularly if it soaks in.

Condensation will often form on external walls in your home – particularly behind furniture such as wardrobes where there is very little airflow.  It is in these areas that real problems can start.

When condensation forms on porous surfaces, it can create damp patches.  As plaster becomes saturated it may start to crumble and cause paint and wallpaper to detach from the surface.  Dark stains may develop as pigment from the plaster soaks through the paint, and if the damp is not dealt with, mould will quickly start to grow.

Even small amounts of mould growing on your bedroom walls and ceilings can start to damage your health.  Mould spores are an allergen that can cause problems for people with respiratory conditions or weakened immune systems.  Some species even release mycotoxins that are dangerous.  Getting rid of condensation reduces the risk of mould growing in your bedroom.

Preventing condensation in your bedroom

The most effective way of preventing condensation in your bedroom is to reduce the amount of humidity in your home.  Practical steps such as ensuring that you close the bathroom door when using the bath or shower and ensuring that your extractor fans are working properly will help, but they won’t affect the water vapour that you exhale at night!

Whole house ventilation systems such as EnviroVent’s ATMOS (a Positive Input Ventilation System) are highly effective at preventing condensation.  These systems work 24 hours a day to circulate air around your home.  They draw in fresh, filtered air from outside and gently release it into your rooms to displace the humid air.  PIV systems can help reduce radon and pollen levels in your home, making it a more pleasant and healthy place to live.

Find out more

If you have discovered condensation on your bedroom windows and are worried about the risk of developing mould, we can help.  Our local ventilation specialists offer a FREE home survey service.  They will visit your home and identify the causes of condensation before advising you about the best way of stopping the problem for good.  Enter your postcode below to find a specialist in your area and stop condensation nor good.

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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