Window condensation in Spain: why it happens and how to stop it
In winter many homes on the Costa Blanca wake up to wet glass on the inside, drops on the frames and black spots in the corners. It is not bad luck: moisture in the air turns into water when it touches a cold surface. Here is what depends on the window, what depends on the house, and what you can do from today.
Updated 19/10/2026
Why the glass gets wet on the inside
Indoor air always carries water vapour: from breathing, showers, cooking and drying clothes. When that air touches a surface colder than its dew point, the vapour condenses into drops. On a window, the coldest parts are the glass and the frame.
On the coast of Alicante and Murcia two things happen at once: the air is humid all year, and many homes were built with single glazing and aluminium frames without a thermal break. Those frames let the outside cold straight through, so at night they cool down and "sweat". On top of that, in winter we open windows less and moisture builds up. Homes that stay closed for weeks while the owners are away suffer most.
Is it the window or the house?
- Drops all over the glass and on the aluminium frame: the window is cold. With single glazing or frames without a thermal break this almost always happens when indoor humidity is high.
- Drops only along the bottom edge of the glass: the edge of a double-glazed unit is its coldest part. Common with older units or metal spacers.
- Water or mist between the two panes: the double-glazed unit has lost its seal. It cannot be cleaned; the glass unit needs replacing.
- Condensation on every window and a damp smell: the main problem is ventilation, not one particular window.
- Drops on the outside of the glass in the morning: a good sign. It happens with highly insulating glass, which keeps the heat inside so its outer face stays cold.
What you can do from today
- Air the house for 10 minutes a day with windows open on opposite sides, ideally mid-morning. It removes moist air without chilling the walls.
- Use the extractor fan when cooking and showering, and keep the bathroom door closed until the steam has gone.
- Do not dry laundry indoors without ventilation: one wet load releases a lot of water into the air.
- Keep the temperature steady instead of heating hard in short bursts; walls and frames cool down less.
- Keep curtains and furniture away from the windows so air can circulate.
- Wipe the drops every morning and treat black spots with a mould cleaner before they spread.
- A cheap hygrometer shows how humid the house is. Constantly above 60–65 %, condensation is almost guaranteed. If you are away for long periods, a dehumidifier on a timer helps a lot.
When to replace the windows
If you ventilate properly and the frames still stream with water every morning, the window is the weak point. Modern windows fix it in three ways:
- Double glazing, and low-emissivity glass if you want more: the inner face of the glass stays mild.
- Insulating frames: multi-chamber PVC or thermally broken aluminium, which stop the cold coming through the frame.
- Properly sealed fitting between frame and wall, so there are no cold bridges or draughts around it.
A very airtight window lets less air through, so you still need to ventilate after replacing windows. Many tilt-and-turn windows have a micro-ventilation position: a small, secure gap that refreshes the air without draughts.
Old aluminium sliding windows condense the most and also let air in. If you replace them, look at the thermally broken or PVC version. Before deciding, check whether your new windows could qualify for a tax deduction, and read our guide to replacing windows in Spain.
How we can help
- Send us a photo of the wet window in the morning on WhatsApp and we will tell you whether it is the window, the glass or the ventilation.
- If only the double-glazed unit has failed, we look at replacing the glass without changing the whole window.
- We make the windows in San Fulgencio and fit them with our own team in Torrevieja, Orihuela Costa, Guardamar, Elche and across the Costa Blanca. We speak English. Get an estimated price in a minute with the calculator.
Frequently asked questions
Is it normal for new windows to have condensation?
On the inside, a little along the bottom of the glass on very cold, humid mornings can happen, especially in bathrooms and bedrooms. If there is a lot, it is usually a lack of ventilation. On the outside of the glass it is normal and means the glass insulates well.
There is water between the two panes. Can it be fixed?
It cannot be dried or cleaned: the seal of the double-glazed unit has failed. The fix is a new glass unit; if the frame is fine, you do not need to replace the whole window.
Does a dehumidifier solve condensation?
It helps a lot in closed-up homes and ground-floor flats because it lowers the humidity. But if the window has single glazing or aluminium without a thermal break, the frame will stay very cold and keep getting wet.
PVC or aluminium against condensation?
Both work if the aluminium has a thermal break. Multi-chamber PVC usually insulates a bit better for the same price; thermally broken aluminium allows slimmer frames and large sliding doors.
How long does it take to replace a window?
For white PVC windows the usual lead time from measuring to fitting is 1 to 2 weeks. A standard window is replaced in a few hours, with no building work.
Are your windows wet every morning?
Send us a photo on WhatsApp and we will tell you whether it is the window, the glass or the ventilation, with an estimated price if replacing makes sense.