Are your windows misted up, cloudy, or letting in draughts?
You could be looking at a blown double glazed unit – a common but fixable problem. At JCarter, we provide fast, affordable replacement glass units in Bournemouth, Poole, Christchurch and across Dorset, helping homeowners restore warmth, clarity and energy efficiency to their homes.
What Is a “Blown” Double Glazed Unit?
Double glazed windows are made from two panes of glass separated by a sealed air or gas-filled cavity. When the seal fails – due to age, temperature changes, or poor installation – moisture enters the space between the panes, causing the unit to become “blown.”
Once blown, the unit loses its insulation value and becomes an eyesore.
5 Warning Signs Your Double Glazing Is Blown
1. Mist or Condensation Between the Panes
This is the most obvious sign. If the fog is between the glass, not on the inside or outside surface, the sealed unit has failed.
Tip: Condensation that can’t be wiped away from either side = blown unit.
2. Cloudy or “Milky” Glass Appearance
Even without visible droplets, you may notice the window looks hazy, fogged, or has a milky stain inside. This is caused by mineral deposits left as moisture evaporates and re-condenses repeatedly.
3. Draughts Around the Frame
A failed unit can sometimes indicate more than just blown glass – it could point to perished seals or warped frames, especially on older UPVC or aluminium windows.
At JCarter, we check the full frame as part of our replacement service.
4. Water Leaks or Damp Patches
If you notice damp around the window reveals, peeling paint, or mould, your glazing could be letting in moisture. This isn’t just a comfort issue – it could lead to structural damage over time.
5. Higher Heating Bills
Blown units allow warm air to escape and cold air to enter. If your bills are rising without explanation, your insulation value may be compromised – especially on north- or east-facing windows.
Should You Replace the Whole Window?
No – in most cases, you don’t need to replace the full window frame. We can replace just the sealed glass unit, making it quicker and cheaper.
| Option | Description | Typical Cost |
|---|---|---|
| Replace whole window | New frame, glazing, trim, and cill | £300–£900+ per window |
| Replace blown glass unit | New sealed unit fitted into existing frame | £60–£150 on average |
We’ll always give you an honest assessment and quote before any work begins.
Common Causes of Blown Glazing
| Cause | Explanation |
|---|---|
| Age (10–20 years) | Natural degradation of the sealant |
| Poor installation | Badly seated frames or wrong spacers |
| Harsh weather | UV, wind and rain can weaken older units |
| Pressure changes | Caused by altitude, storms or incorrect venting |
Can You Repair a Blown Window?
You may see DIY kits advertised online, but these are not permanent fixes. Drilling holes or vacuuming moisture voids any warranty and won’t restore energy performance.
The only long-term solution is replacing the sealed unit.
Areas We Cover
Our glazing repair and blown unit replacement services are available throughout:
- Bournemouth
- Poole
- Christchurch
- Ferndown
- Wimborne
- Southbourne
- Ringwood
- And surrounding Dorset towns
Looking for a glazier near me? JCarter can help today.
