Quick Answer
Condensation on the inside surface = cold glass + warm moist air. Fix with ventilation or better glazing. Between the panes = failed sealed unit, needs replacing. On the outside = actually a good sign — it means your glazing is working.
The Three Types of Window Condensation
1. Interior Condensation (on the room side)
The most common type. Warm, moist air from cooking, showering, breathing, and drying clothes meets the cold window surface and the moisture condenses. It’s worse on single-glazed or old double-glazed windows because the inner pane gets colder.
Fix: Improve ventilation (open trickle vents, use extractors) and/or upgrade glazing. Modern double glazing keeps the inner pane warmer, dramatically reducing condensation.
2. Condensation Between the Panes
This means the sealed unit has failed. The airtight seal between the two panes of glass has broken, allowing moist air in. Once inside, it condenses and creates a permanent foggy or misty appearance.
Fix: Replace the sealed glazing unit. The frame is usually fine — just the glass unit needs changing. Cost: £80–£200 per unit depending on size.
3. Exterior Condensation (on the outside)
Surprising but actually a good sign. External condensation happens when the outer pane of glass is so well insulated that it stays cool while the inner pane stays warm. It means your glazing is working efficiently — very little heat is getting through to the outer pane. Common with modern low-E glass coatings.
Fix: None needed. It evaporates as the sun warms the glass. This only happens on high-performance glazing.
When Condensation Means You Need New Windows
Interior condensation alone does not always mean new windows. But in combination with other signs, it points that way:
- Heavy daily condensation that drips onto the sill and causes paint to peel or timber to rot
- Condensation combined with draughts — the window is both cold and leaky
- Mould growing around the window frame from sustained moisture
- Failed sealed units (misting between panes) in multiple windows
- Single-glazed windows — always worth upgrading for thermal and condensation reasons
| Window Type | Inner Pane Temp (0°C outside) | Condensation Risk |
|---|---|---|
| Single glazed | 1–3°C | Very high |
| Old double glazing (pre-2002) | 8–11°C | Moderate |
| Modern double glazing (low-E, argon) | 15–17°C | Low |
| Triple glazing | 17–19°C | Very low |
Upgrade to Condensation-Free Windows
Modern double or triple glazed timber windows keep the inner pane warm enough to prevent condensation. Configure yours and see the price.
Open the 3D Configurator Book a SurveyQuick Fixes for Condensation (Without New Windows)
- Open trickle vents — those small slots at the top of the window are there for a reason
- Run extractor fans — during and 15 minutes after cooking/showering
- Don’t dry clothes on radiators — a single load adds 5 litres of moisture to the air
- Keep low background heating — a constant 15°C overnight is better than off/on cycles
- Open windows briefly — 5 minutes of fresh air exchange clears moisture without cooling the house significantly
Frequently Asked Questions
Why do my windows get condensation in the morning?
Overnight, room temperature drops and the window glass becomes the coldest surface. Moisture in the air condenses on the cold glass. It is worse in bedrooms because breathing adds moisture. Better ventilation and improved glazing both reduce it.
Is condensation on the inside of windows normal?
Some interior condensation is normal in cold weather, especially with single glazing or old double glazing. If it happens daily or in large amounts, it indicates either too much humidity in the home or windows with poor thermal performance.
What does condensation between the glass panes mean?
Condensation between the panes means the sealed unit has failed — the seal has broken and moist air has entered the gap. The unit needs replacing. This is not a window frame issue — just the glass unit.
Will new windows stop condensation?
New double or triple glazed windows significantly reduce interior condensation because the inner pane stays warmer. They will not eliminate it entirely if the home has very high humidity from cooking, drying clothes indoors, or poor ventilation.
How do I reduce condensation without replacing windows?
Open trickle vents, use extractor fans in kitchens and bathrooms, avoid drying clothes on radiators, and keep heating on low overnight rather than letting the house go cold. A dehumidifier helps in severe cases.