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Published on October 21, 2023 7:05 AM

If you’ve ever woken up on a chilly morning and couldn’t see through your bedroom window due to foggy condensation, you’re not alone. Many people face the issue of window condensation, particularly in double-glazed windows, during colder months. This seemingly small nuisance actually touches upon principles of physics and requires a multi-faceted approach to resolve.

I remember when I was growing up we had single glazed steel windows and in the bedrooms they were covered in condensation in the morning. It was just a fact of life. There was no such thing as double glazing! Later in life when I started building and refurbishing property the new casement windows and uPVC sash windows would be full of condensation as the new plaster work was drying out.

Why Does Condensation Occur on Windows?

At Colin’s Sash Windows we occasionally get emails from customers who’ve fitted our double glazed sash windows and they’re confused because they’re getting condensation. They think there’s a fault with the windows which we need to address. At the time of writing in October 2023 we’re coming into the colder, wetter months when condensation if rife.

Condensation on windows, even if they’re double-glazed, occurs when warm, moist air collides with the cooler glass surface, transforming water vapour into liquid droplets. This process hinges on the concept of the “dew point,” a temperature at which air becomes saturated with moisture and releases it as condensation.

The phenomenon is particularly noticeable in residential spaces where various activities contribute to increased indoor humidity levels. For instance, cooking, showering, or even the act of breathing release moisture into the air. During winter, the air inside your home is warmed by your heating system, increasing its capacity to hold moisture. However, the windows, particularly the inner pane, remain significantly cooler because they are in direct contact with the colder outside environment. This temperature disparity creates the perfect stage for condensation, as the warm, moisture-heavy air inside cools upon reaching the colder glass surface, hitting the dew point, and releasing water droplets.

Strategies to Prevent Window Condensation

Preventing window condensation involves reducing indoor humidity, improving ventilation, and maintaining a consistent indoor temperature.

  • Extractor fans can effectively control moisture levels, especially in high-humidity areas like kitchens and bathrooms. If you don’t have an extractor fan in your bathroom it’s good practice to leave the trickle vents open all the time.
  • Opening windows briefly, even in winter, allows fresh air to circulate and helps in expelling moist air from the inside.
  • Under recent UK Government regulations nearly all new windows need to have trickle vents which help reduce the likelihood of condensation forming on the inside of windows by allowing moist air to escape. Most of our windows and doors are now supplied with trickle vents including our very popular heritage French doors. Lot’s of our customers don’t really like the look of them but the benefits definitely outweigh the negatives.

Maintaining moderate and consistent temperatures within your home is also critical. Sudden drops in temperature during the night or in specific parts of the home can exacerbate condensation issues. Solutions include using blinds or curtains to add an extra layer of insulation and redirecting warm air from heating systems towards the windows to reduce the temperature difference.

Condensation: A Bigger Problem in Bedrooms?

Interestingly, condensation problems often seem more pronounced in bedrooms. This occurrence is due to a combination of factors, including human presence and room conditions at night. Bedrooms usually have reduced ventilation, with windows often closed and doors shut, trapping in the humid air. Additionally, while sleeping, people exhale moisture and perspire, contributing to higher room humidity levels.

The situation compounds when heating levels drop at night. Many households lower their heating to save energy or to avoid overly warm sleeping conditions, inadvertently creating the perfect condensation scenario: cooler window surfaces and warm, moist indoor air. This balance is delicate, and a few degrees difference can tip the scales, leading to increased condensation.

Furthermore, blinds and curtains, common in bedrooms for privacy and light control, can create pockets of cooler air around windows, further encouraging condensation. The limited airflow doesn’t help, as it allows the moisture-laden air to settle on surfaces like the cool glass of a window.

Conclusion: Balancing Your Home Environment

Combating condensation on your double-glazed windows requires a holistic approach that encompasses understanding the underlying science and adapting your home environment’s dynamics. By controlling the humidity levels, ensuring adequate ventilation, and maintaining a stable temperature in your living spaces, you can significantly reduce or even eliminate unwanted condensation.

It’s equally important to adjust your strategies based on different room usages. For instance, being mindful of ventilation and warmth in bedrooms is crucial due to the unique conditions contributing to moisture build-up in these spaces.

Remember, the goal isn’t just clearer windows; it’s about creating a healthier, more comfortable living environment. Consistent temperatures, controlled humidity, and good air quality can benefit everything from your home’s structural integrity to your own respiratory health and comfort. In the battle against condensation, knowledge and a little proactive management go a long way.

Colin Greenslade
Written by Colin Greenslade
I'm the founder of Colin's Sash Windows. I disrupted the sash windows market in the UK in 2014 by introducing fixed prices for uPVC sash windows in the UK. Before this they were generally only available at very high prices through window installers. Today our business is one of the market leaders in supply only windows, doors and roofs in the UK.

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