How to stop condensation on double glazed windows

• June 20, 2026|
• Windows

Condensation on double glazed windows is one of the most common complaints from homeowners across the North West.

The short answer: if it’s on the inside surface, you can usually manage it yourself. If it’s between the panes of glass, the window seal has failed and the only real fix is replacement.

Read on for the full picture.

Why condensation forms on windows

Condensation forms when warm, moist air meets a cold surface. When the glass drops below the dew point – the temperature at which air can no longer hold its water vapour – that moisture turns into water droplets on the window surface.

In UK homes, the colder months create the perfect conditions: high indoor humidity from cooking, showering, and even breathing, combined with cold glass panes chilled by low outdoor temperatures. The greater the temperature difference between inside and outside, the higher the likelihood of condensation.

Double glazing reduces this problem significantly. The air gap between the two panes of glass acts as a thermal buffer, keeping the inner glass closer to room temperature. But it doesn’t eliminate condensation entirely – and when it appears, the location tells you everything.

Inside, outside, or between the panes? What each type means

Where the condensation appears changes everything about how you tackle it.

Condensation on the inside of windows

This is the most common issue. Humid indoor air hits the cold glass surface and water droplets form. It’s a ventilation and lifestyle problem, not a window fault.

Condensation on the outside of the glass

External condensation is actually a good sign. It means your double glazing is doing its job – insulating so well that little warmth reaches the outer pane, leaving it cool enough for moisture in the early morning air to settle on it. It clears once the sun rises and air warms up. No action needed.

Condensation between the panes of glass

This is the serious one. If you can see fogging or water droplets in the air gap between the two glass panes, the sealed unit has failed. The airtight seal has broken down, the insulating gas has escaped, and moist air has entered the cavity. No amount of ventilation or dehumidifying will fix this. The only genuine solution is to replace the sealed unit or the full window.

How to stop condensation on the inside of your windows

If your problem is surface condensation on the inside of the glass, the causes of condensation come down to excess moisture in the air and poor air circulation. Here’s what actually works.

1. Improve ventilation throughout the home

Proper ventilation is the single most effective way to reduce indoor humidity. Open windows briefly each morning – even ten minutes – to let moist air out and fresh air in. In kitchens and bathrooms, use extractor fans every time you cook or shower, and keep them running for a few minutes after you’re done. Leave the bathroom door closed while showering to stop humid air spreading through the house.

If you can’t open windows easily, consider having trickle vents fitted. These small vents built into window frames allow a controlled flow of fresh air without compromising security or heat loss significantly.

2. Reduce indoor humidity at the source

A few simple changes make a noticeable difference to moisture levels:

• Don’t dry clothes indoors if you can help it. A single load adds around 2 litres of water vapour to your home’s air.
• Cover pots when cooking to contain steam.
• Move houseplants away from window sills – they contribute to high humidity levels.
• Use a dehumidifier in rooms prone to moisture build-up, such as bedrooms or living rooms where the windows often mist up overnight.

3. Keep room temperature consistent

Sudden changes in temperature worsen condensation. Rather than letting rooms go cold and then blasting the heating, maintain a low, steady temperature throughout the day. This keeps the window surface warmer and reduces the temperature difference between the glass and the air inside.

4. Pull curtains and blinds back

Heavy curtains trap cold air against the glass, lowering the window surface temperature even further. Pulling them back – especially overnight – improves air circulation around the window panes and reduces the amount of condensation that forms.

When ventilation isn’t enough: Failed window seals

If you’ve tried all of the above and still have misting inside the double-glazed unit itself, you’re dealing with a failed window seal – not a ventilation problem.

Over time, the rubber seals around sealed units degrade due to age, UV exposure, or poor original manufacture. Once the seal breaks, moisture-laden air enters the air gap between the panes and you get the characteristic fogging that won’t wipe away. The thermal performance of the unit drops and – in windows fitted with low-emissivity glass – so does their ability to reflect heat back into the room, directly impacting your energy bills.

There is no DIY fix for this. Drilling holes in the glass to dry out the cavity, a technique sometimes suggested online, is a temporary workaround at best and damages the unit further. Re-sealing from the outside doesn’t work because the desiccant inside the spacer bar is already saturated with moisture.

The only way to restore a failed unit is to replace the sealed unit or, if the frames are old and the seals have gone on multiple windows, to replace the windows entirely.

New uPVC windows: The long-term fix for persistent condensation problems

If your windows are ageing and you’re seeing condensation issues across multiple panes, new windows are worth serious consideration. Modern A-rated uPVC windows are built to a fundamentally different standard than older double glazing.

At Weather Shield North West, we install multi-chambered uPVC frames with Pilkington K Glass™ and Super Spacer® warm edge technology. The warm edge spacer bar reduces the cold bridge around the perimeter of the glass – the area most prone to condensation forming – and the low-emissivity coating reflects heat back into the room rather than letting it escape through the glass.

The result is a warmer inner glass surface, lower humidity levels at the window, and far less likelihood of condensation forming – even in the colder months.

Working with Weather Shield North West

Weather Shield North West has been helping homeowners across Bolton, Bury, Wigan, Preston, Stockport and the wider Greater Manchester area get on top of condensation issues for over 20 years.

Our A-rated uPVC windows with warm edge technology address the root cause rather than the symptoms, and every installation is backed by a 10-year guarantee.

Get your free, no-obligation quote today – or call us on 01204 308731 to talk it through with the team.