Why Do Double-Glazed Windows Mist Up Inside?
If you’ve noticed cloudy or foggy patches between the panes of your double-glazed windows, you’re not alone. This is one of the most common issues UK homeowners face with older or damaged units. Let’s look into what causes this and what your options are for fixing it.
What Causes Misting Between the Glass?
The mist or fog you see forming inside your double glazing happens when the airtight seal around the glass unit fails. Here’s why it occurs:
- Seal failure: Over time, the seal around the unit may shrink, crack, or break, letting in moisture.
- Age and wear: Most double-glazed units have a lifespan of 10–20 years. Older units are more prone to failure.
- Poor installation: If the unit wasn’t sealed properly from the start, it’s more likely to mist up early on.
- Temperature changes: Extreme hot and cold can cause the materials to expand and contract, weakening the seal over time.
Why It’s Not Just Moisture on the Surface
It’s easy to confuse external condensation (on the inner or outer surface of the glass) with internal misting. But here’s how you can tell:
- Surface condensation can be wiped away. Misting inside the glass can’t.
- If the mist appears trapped between the panes, it’s a sign the sealed unit has failed.
Can Misted Double Glazing Be Repaired?
Yes – in most cases, you don’t need to replace the whole window.
Glass-Only Replacement
This is the most cost-effective and practical solution. A professional can replace just the sealed glass unit, keeping your existing frames intact. This is quicker, cheaper, and less disruptive than full window replacement.
When Full Window Replacement Is Needed
- If your frames are warped, cracked, or rotten
- If you’d like to upgrade to a new frame material (e.g., move from uPVC to aluminium)
- If the damage affects the structural integrity of the whole window
In most cases, glass-only replacement is all that’s needed – especially with strong existing uPVC or aluminium frames.
The Impact on Your Home
- Reduced energy efficiency: A failed unit no longer insulates properly, so your home may feel colder and your bills creep up.
- Moisture risks: Persistent internal condensation can encourage mould or mildew nearby.
- Ruins the view: Nobody enjoys looking out through a steamed-up window.
How Get My Windows Fixed Can Help
We specialise in replacing misted double-glazed units across the UK. Our expert team can:
- Assess the issue with a no-pressure on-site survey
- Replace just the failed glass unit – not the whole frame
- Offer clear pricing and fast turnaround times
- Provide high-performance, energy-efficient sealed units
You’ll be surprised how quickly we can restore your view and stop the energy loss – often within just a few days from first visit to installation.
What You Can Do Now
DIY Checks
- Wipe the inside and outside of the glass – if the mist stays, it’s internal
- Check the seals (rubber or plastic beads) for cracks or separation
- Look for signs of moisture or mould near the window frame
Time to Act?
If you’re dealing with a misted-up view, colder room temperatures, or rising bills, it’s worth looking into fixing the problem now – before it gets worse or spreads to other windows.