Condensation on windows: what a curtain can do, and what it makes worse
Condensation on the inside of a window appears when humid air meets a surface that is cold enough. A closed curtain can encourage it by limiting the warming of the glass and the circulation of air near it.
Keep an eye on humidity, keep airing and ventilating, and do not let the fabric touch a wet surface. Leaving space behind the curtain can help air circulate, but it does not guarantee that the condensation will go away.
Where the water on the glass comes from
Condensation depends on the temperature of the surface and the humidity of the air. When the glass becomes cold enough, the water vapour in the air can settle on it as droplets.
It is common in cold periods, but it is not limited to autumn or winter. Cooking, showers and drying laundry can increase indoor humidity.
What the curtain can do, and what it makes worse
As Natural Resources Canada explains, closed curtains can limit air circulation near the window and encourage condensation. The effect also depends on the glazing, the temperatures and the humidity.
| Situation | Effect on condensation |
|---|---|
| Curtain pressed against the glass, closed day and night | Can encourage condensation by limiting the warming of the glass and air circulation. |
| Curtain with space behind it, open during the day | Can improve air circulation; check whether the condensation persists. |
| Curtain that also covers the wall around the window | The coverage can improve comfort, but does not show that the risk of condensation goes away. |
The curtain can improve comfort near the window. It does not dehumidify the air and is no substitute for finding the cause of persistent humidity.
Habits to check every day
Start with airing, ventilation and the sources of humidity. If the problem persists, the window or the ventilation may need to be checked.
| Habit | Why |
|---|---|
| Open the windows wide for 5 to 10 minutes every day | Brief airing renews the air. It complements ventilation that works; it is not always enough to solve excessive humidity. |
| Deal with the source before the glass | Drying laundry indoors, cooking without a lid, a bathroom without an extractor: the glass only reveals the problem. |
| Do not press the curtain against the glass | Leave space between the fabric and the glass, and open it during the day when the sun is out. |
When the window itself is the cause
Persistent misting between the panes of double glazing can indicate a fault in the glazing unit: have it inspected. On the inside surface, look at the causes linked to humidity, air circulation and glass temperature together.
The ADEME winter guide stresses the importance of airing even in winter and of checking that the ventilation works if humidity is excessive. Do not block air inlets and outlets with the curtain.
Frequently asked questions
Does a thermal curtain cause condensation?
The curtain can encourage condensation by keeping a colder zone near the glass and limiting air circulation. Opening the curtain and keeping an eye on the glass helps you monitor the problem, without guaranteeing it will be solved.
Should I take my curtains down in winter because of humidity?
It is not always necessary to take them down. If the fabric is damp or mouldy, move it away from the wet surface and deal with the cause. Persistent humidity calls for a check of the ventilation and the window.
Why does condensation mostly appear in the morning?
During the night, the glass can cool down while humidity builds up in the room. The result depends on the heating, the ventilation and the outdoor conditions.
Does condensation damage curtains?
Prolonged contact with a damp surface can stain the fabric and encourage mould. Keep the curtain dry, follow its care instructions and have the cause investigated if the humidity comes back.
To prepare for the cold season, our autumn curtains page brings together the September tips, and our made-to-measure thermal curtains are made to your dimensions in 620 g/m².
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