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How to Remove Condensation in Double Glazed Windows

Last modified: 17.01.2024
Close-up of condensation build-up on a window. This is often a sign of poor ventilation or thermal bridging. EWI Store offers breathable, vapour-permeable insulation systems that help regulate indoor humidity and reduce condensation for healthier indoor environments.

Condensation in double-glazed windows can be a common and frustrating problem, particularly during the colder months. Not only does it obstruct your view, but it can also lead to mould and mildew, which are harmful to your home and your health. Understanding the causes and finding effective solutions to this issue is essential for maintaining a comfortable and healthy living environment.

Condensation in double-glazed windows is a phenomenon that's both common and perplexing, particularly in environments with stark differences between indoor and outdoor temperatures. Condensation occurs when moisture-laden air comes into contact with a colder surface, causing the water vapour to turn into liquid. This is because cold air holds less moisture than warm air. In the case of double-glazed windows, this typically happens when the warm, humid air inside your house meets the cold surface of the window glass. Double-glazed windows consist of two layers of glass separated by a space that is usually filled with air or an inert gas like argon. This design creates an insulating barrier, reducing heat loss through the windows. While effective for insulation, this setup can inadvertently create an ideal surface for condensation under certain conditions.

Several factors can contribute to the development of condensation in double-glazed windows:

  1. Internal Condensation: This occurs on the interior pane of the window and is a direct result of high indoor humidity levels.
  2. External Condensation: This forms on the outside pane and is more common in newer, highly energy-efficient windows. It typically indicates that the window is effectively preventing heat transfer.
  3. Condensation Between Panes: This is an indication that the seal of the double glazing has failed, allowing moisture to enter the space between the panes.

Condensation in double-glazed windows can lead to several significant issues, impacting both the functionality and health of your home environment. One of the immediate problems is the reduction in visibility and natural light penetration. Condensation blurs the glass, diminishing the aesthetic appeal and the welcoming ambience created by natural light. This issue extends beyond mere inconvenience; persistent moisture can cause substantial damage to window frames and sills, particularly if they're wooden. Over time, this can lead to rot, warping, and even mould growth, which not only damages the structure but also poses health risks. Mould and mildew, fostered by the damp conditions, can release allergens and irritants, potentially affecting those with allergies or respiratory issues. Moreover, double-glazed windows are designed to enhance a home's energy efficiency by reducing heat loss. However, condensation, especially between the panes, can signal a failure in the window’s sealing, leading to escaped insulating gases and decreased thermal efficiency. This can result in higher energy bills due to increased heating requirements. In extreme cases, the persistent moisture from condensation can cause more extensive structural damage, impacting plaster, paint, and other adjacent materials, leading to costly repairs. Additionally, the longevity of the windows themselves can be compromised, necessitating premature replacement. Addressing condensation in double-glazed windows is therefore essential, not only for maintaining the aesthetics and comfort of your home but also for preserving its structural integrity and ensuring a healthy living environment.

Improving the ventilation in your home is key. Open windows regularly to allow moist air to escape and fresh air to circulate, especially in high-humidity areas like kitchens and bathrooms. A dehumidifier can significantly reduce moisture levels in your home, thus preventing condensation on windows. Maintaining a consistent temperature in your home helps to reduce condensation. Sudden temperature changes can exacerbate the problem. Some houseplants, such as peace lilies and spider plants, are known to reduce humidity in the air.

External condensation is less common and typically occurs during specific weather conditions. It usually disappears as the day warms up and isn't a sign of a faulty window. Low-emissivity (Low-E) glass can help reduce external condensation by reflecting heat into the home, keeping the external pane warmer.

Condensation between the panes of double-glazed windows is a problem that signifies a deeper issue with the window unit itself. Over time, double-glazed windows, like all things, deteriorate. The rate at which this happens largely depends on the build quality of the windows. A common reason for condensation in these windows is the degradation of the seal that forms the 'sealed unit' between the two panes of glass. As this seal begins to degrade and crack, it allows moist air to enter the 'air gap' between the panes, leading to condensation. In older or lower-quality units, the issue is often exacerbated by the use of substandard sealants, such as a basic strip of rubber, which can loosen over time. Furthermore, if the seal and bead meant to hold the glass in the frame deteriorate, moisture can seep into the frame, eventually affecting the 'air gap' seal. In some cases, even the uPVC frames may crack, allowing water to accumulate. A pivotal component in double-glazing units is the 'spacer' bar, filled with a desiccant material designed to absorb moisture in the 'air gap'. However, if the seal is even slightly imperfect, the desiccant can become saturated, and when it can no longer absorb moisture, condensation appears. Often, this issue has been present for a while but only becomes noticeable when the desiccant stops functioning effectively.

Condensation in double glazing not only is a nuisance but also signifies that costly heat is escaping from your home. If you notice condensation, moisture, or significant water between the panes, likely, that the seal has completely failed, and the units are no longer functioning as intended.

In cases where the uPVC units are still in good condition, it may be possible to just replace the sealed units. There are specialist companies that can repair or recondition each faulty unit. Typically, this involves drilling a hole into the spacer bar or glass pane unit, injecting a drying agent or desiccant to dry out the air and expel the condensation, and sometimes using an anti-fogging agent to prevent future moisture build-up. The unit is then resealed. However, while resealing may resolve the immediate issue, it doesn’t always address the underlying cause of the seal failure. Therefore, before opting for a repair, consider whether the benefits and expected lifespan justify the cost.

Replacing the units, although more expensive, often offers better long-term value. If your double glazing is less than 10 years old, check if there’s a guarantee. Should a guarantee exist, contact the installing company for potential free replacement if the seal or unit is defective. It's crucial not to tamper with the units or attempt DIY repairs, as this can invalidate the guarantee. Modern, reputable window companies typically manufacture units to high standards, with newer installations boasting long lifespans (sometimes up to 15 or 20 years). Installing A-rated windows has become standard practice for many, as they reduce condensation by minimising heat loss and capturing heat from the sun, thereby also reducing energy bills.