Window Condensation: What Causes It and How to Fix It
Condensation on windows is one of the most common complaints from homeowners in {location}, especially during the colder months. It can lead to mould, damage to window frames and a general feeling that something is wrong with your glazing. But condensation isn't always a sign of faulty windows — and the fix is often simpler than you think.
Why Condensation Forms
Condensation occurs when warm, moist air meets a cold surface. The moisture in the air turns into water droplets on the coldest surface it can find — usually your windows. The more moisture in the air and the colder the glass, the worse the condensation.
Common sources of indoor moisture include:
- Cooking without using an extractor fan
- Drying clothes indoors on radiators or airers
- Hot showers and baths without adequate ventilation
- Breathing — a family of four produces around 8 litres of moisture per day just by being at home
- Gas heaters that aren't flued to the outside
The Three Types of Window Condensation
Inside surface condensation is the most common type. It forms on the room-facing side of the glass, usually overnight when temperatures drop. This is a ventilation and humidity problem, not a window fault.
Condensation between the panes means the sealed unit has failed. The perimeter seal has broken down, allowing moist air into the gap between the two panes of glass. This cannot be wiped away and the unit needs replacing.
Outside surface condensation actually indicates your windows are working well. It happens when the outer pane is colder than the outside air — a sign that very little heat is escaping through the glass. This is most common with high-performance low-emissivity glazing and disappears as the sun warms the glass.
How to Reduce Indoor Condensation
- Ventilate properly: Use trickle vents on your windows — they're there for a reason. Open them during the day, especially in kitchens and bathrooms.
- Use extractor fans: Run kitchen and bathroom extractors during and for 15 minutes after cooking or showering.
- Avoid drying clothes indoors: If you must, do it in a room with the window slightly open or a dehumidifier running.
- Maintain consistent heating: Keeping your home at a steady low temperature is better than blasting the heating intermittently, as it keeps surfaces warmer.
- Consider a dehumidifier: In older or poorly ventilated properties in {location}, a dehumidifier can make a dramatic difference.
When to Call a Professional
If condensation appears between the panes, the sealed unit has failed and needs replacing. A glazier in {location} can usually replace just the glass unit without changing the whole frame, saving considerable cost.
If you're getting persistent heavy condensation despite good ventilation habits, it's worth having a window installer check that your trickle vents are open and functioning, your seals are intact, and the windows were installed correctly. Poorly fitted windows can create cold spots that attract condensation.
Key Takeaway
Most window condensation is a lifestyle and ventilation issue, not a window fault. Before spending money on replacements, try improving ventilation for a few weeks. If the problem persists, get a professional assessment from a FENSA-registered installer in {location}.