Why Do Double-Glazed Windows Mist Up Inside?
If you’ve ever noticed a foggy or misty patch inside your double-glazed windows that doesn’t wipe away from either side, you’re not alone. This is a common issue in UK homes—and it’s usually a sign that something’s not quite right with the sealed glass unit.
What Causes Internal Condensation in Double Glazing?
When double-glazed windows mist up inside the glass unit (between the panes rather than on the surface), it usually means the seal has failed. Normal double-glazing contains two panes of glass with an airtight space in the middle, often filled with an inert gas like argon. This space acts as insulation—but only if it remains sealed.
Once the edge seal breaks down, moisture from the air can slip into the cavity. Over time, this builds up as condensation between the panes. Because the water’s trapped inside, you can’t wipe it away—and it leaves the glass looking dirty or misty, and less effective thermally.
Common Causes of Seal Failure
Seals can break for many reasons, including:
- Age: Most double-glazed units last 10–20 years before seals start to naturally degrade.
- Poor installation: If the original glazing wasn’t installed correctly, seal wear can happen much sooner.
- Temperature changes: Daily expansion and contraction from heat and cold cause stress on the seals.
- Bad drainage: If water collects around your window frames, it can encourage the seals to fail.
Is Misting Just Cosmetic?
Not at all. While it can be unsightly, misted windows also mean reduced energy efficiency. When the sealed unit fails, the insulating gas escapes and is replaced by moist air. This makes your window less effective at keeping in heat and blocking noise. Over time, that can mean higher heating bills and a colder home.
Repair vs Replacement: What Can Be Done?
Can You Repair Misted Double Glazing?
In most cases, the sealed glass unit needs to be replaced. The good news is, you don’t need to replace the whole window—including the frame. A reputable glazier like Get My Windows Fixed can replace just the glass, matching the size and style precisely, and restoring clarity and insulation.
What About Full Window Replacement?
You’ll only need to replace the whole window frame if it’s damaged, rotten, or beyond repair. uPVC and aluminium frames often last for years even after the glass unit inside fails. So in most cases, a cost-effective glass-only replacement is all that’s needed.
How Much Does It Cost?
Prices vary depending on window size and type, but to give you a ballpark:
- Standard double-glazed glass replacement: From £80–£150 per unit
- Special shapes or toughened safety glass: Higher, depending on specs
At Get My Windows Fixed, we offer free, no-obligation quotes and don’t charge callout fees. That way, you know exactly what you’ll pay—no surprises.
How to Check If Your Windows Have Failed
Here are a few simple signs to look for around your home:
- Visible misting or clouding between the panes
- Droplets or streaks you can’t clean from inside or out
- A cold draught despite the window being closed
- Discoloured or warped seals around the glass edge
If you’re unsure, don’t worry. One of our local friendly glaziers can inspect the window and let you know the best option—for free.
A Clear Way Forward
Misted double glazing doesn’t just spoil your view—it drains warmth from your home and your wallet. Fortunately, repair is often straightforward, and most frames can stay in place. Glass-only replacement is usually the best-value approach, and it can restore your windows to full clarity and performance quickly.
Contact Get My Windows Fixed today to arrange a free quote and bring your windows back to life.