During the winter, it’s not unusual to wake up in the morning and see large amounts of condensation on your windows. This forms during the night, and it’s not always clear what the cause is. Seeing condensation on your bedroom windows in the morning can be a sign that your home has poor ventilation. If left unchecked, the condensation can soak into nearby walls causing damp, and if you have wooden window frames, it can cause them to rot, leading to an expensive repair bill.
The air in your home contains water vapour that it picks up during the day. Many household activities such as bathing and cooking release steam into the air. The amount of water vapour the air can hold depends on the temperature. At 20oC, a cubic metre of air will hold approximately 17g of water; however at 10oC, the air can only hold 9g of water.
At night, with the heating off in our homes, the amount of moisture that is carried by the air drops, and the excess water vapour forms as condensation on cold surfaces. In a 4mx4mx2m room, the difference in air temperature from 20oC to 10oC overnight will result in at least 250ml of water being released as condensation.
The actual amount of condensation that can form overnight can be much higher than this because, during the night, our breathing and other household activities can release additional water vapour into the air. Depending on the humidity levels in your home, and the number of people in each bedroom, more than a litre of water could end up as condensation on your windows and walls by morning.
If you’ve noticed condensation on your bedroom windows in the morning, there are likely to be three leading causes.
If you bathe or shower before going to bed at night, the steam from your bathroom can spread through your home and raise the humidity levels sharply just as the building starts to cool down. This can be a major contributor to the amount of condensation you will see in the morning – an average bath will release about 600ml of water into the air in the form of steam, and if you don’t have adequate bathroom ventilation, it will spread throughout your home.
Many people dry their towels on radiators in bedrooms. This can be a significant contributor to the amount of condensation that can form in your bedroom. A wet towel might have as much as a litre of water soaked into it. Overnight on a radiator, this can evaporate into the air and worsen your condensation problems.
The leading cause of condensation in bedrooms, though is breathing! Each time you live, a small amount of water vapour is exhaled along with CO2. Each person sleeping in a bedroom will contribute about 200ml of water into the air overnight. This constant addition of moisture means that the air in the room is constantly shedding water onto windows and walls and adding to your condensation problem.
Fortunately, you don’t need to stop breathing overnight or incur the expense of running your heating 24 hours a day to prevent condensation from building up, but you might need to make some minor changes to your behaviour.
Rather than drying towels on your bedroom radiator, use a towel rack in your bathroom. Bathrooms are typically tiled or painted with moisture-resistant paint, so condensation isn’t usually as much of a problem as it can be in a bedroom and is less likely to cause damp patches to form.
If you are taking a bath before bed, it’s a good idea to start filling the bathtub with cold water and then top it up with hot water afterwards. This reduces the amount of steam produced while the bath is filling and can significantly affect how much condensation will form overnight.
In addition to starting to fill the bath with cold water, you should also ensure that you run your extractor fan throughout the time you’re in the tub and for at least half an hour afterwards to help remove the moist air from your home. Modern extractor fans such as the EnviroVent Cyclone 7 include a humidity sensor which adjusts their power level to speed up the extraction process and reduce moisture levels faster.
Read more tips to reduce condensation in your home>>
It doesn’t take long for condensation to develop into damp and mould, which can be expensive to resolve and are a risk to your health, so removing the problem as soon as possible is essential.
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