Last Updated on October 24, 2026 by Umar Farooq
How to stop condensation on windows: lower the humidity in the room and keep the glass warmer: ventilate while you cook and wash, open the curtains by day, and add a dehumidifier only if the room still reads above 50%. Wiping the pane is the symptom treatment. Everything below is the cure.
Most advice online is a flat list of tips. I would rather give you an order, because the free fixes work more often than anyone selling you a gadget admits.
Measure the room before you change it
Condensation needs two things: damp air and a cold surface. Why it forms is covered in the sister guide, so I will not repeat it. What matters here is that you can only fix the half you can see, and a hygrometer shows you the half you cannot.
Put one in the room that mists, read it first thing in the morning, and write the number down. EPA recommends keeping indoor relative humidity below 60%, ideally between 30% and 50%, and says condensation can be a sign of high humidity. Andersen Windows suggests aiming lower in deep winter, around 30 to 35%. If you are already at 40%, buying anything is a waste of money and the glass is the problem, not the air.
How to stop condensation on windows: seven fixes, cheapest first
- Make less steam. Cook with lids on and turn the heat down once it boils. A London council’s tenant guide also suggests running cold water into the bath before hot, which it says cuts the steam by 90%. I have not tested that figure, but the logic is sound: less hot surface, less vapour.
- Stop drying washing on radiators. A radiator rack of wet laundry is the most efficient humidifier most homes own. Dry outdoors, or in a closed room with the extractor running. The full routine is a separate job.
- Run the extractor, and keep the door shut. Fans only work if the steam goes out of the house rather than into the hallway. Leave it on until the mirror is clear, and a little longer.
- Open a window for five to ten minutes. Do it when the air outside is drier than inside, which on a cold, dry day it nearly always is. Trickle vents should stay open and unblocked.
- Open blinds and curtains by day. Closed heavy curtains trap warm damp air against cold glass, so the pane stays cold all night. Andersen makes the same point: open them so warm air can reach the window.
- Keep a little background heat on. A glass pane in a room that swings from hot to cold gets wet every time it cools. Steady, low heat keeps the surface above the dew point. I cannot give you a universal temperature, because it depends on your glazing.
- Add a dehumidifier. Last, not first. More on that below.
Stop condensation on windows overnight
Bedrooms are the hardest case, because you are the moisture source for eight hours with the door shut. The reliable options are a cracked window or open trickle vent, the door slightly ajar, and a dehumidifier running on a timer.
Anti-condensation film, spray and window-sill absorber strips are sold for this. One window retailer lists them, along with a vinegar-and-water wipe, and I found no independent test showing any of them works, so treat them as unproven. An absorber holds a small, fixed amount of water and has to be emptied or replaced; it is a patch for a few mornings, not a fix.
When a dehumidifier is worth it, and when it is not
My firm view: a dehumidifier is the last lever, not the first. It fixes the moisture half and nothing else, and it costs money to run.
Buy one when you have done steps 1 to 6 and the hygrometer still reads above 50%. Skip it when the number is already fine, because then the glass is the cold part and drying the air will not change that. If you are weighing it up, the dehumidifier-for-condensation guide goes through the numbers, the sizing guide covers capacity, and a quiet dehumidifier for the bedroom is the sensible shortlist for night use.
Use this table to match what you see to the right first move:
| What you see | Likely cause | First move |
|---|---|---|
| Wet every morning, all windows | Humid air | Fixes 1 to 4, then a hygrometer check |
| Wet on one cold window only | Cold glass or cold wall | Open the curtains, add heat |
| Wet in the bedroom only | Overnight breathing | Trickle vent, ajar door |
| Hygrometer below 45%, still wet | The window itself | Look at the glazing |
| Fog between the panes | Failed sealed unit | Replace the unit |
When wiping is the wrong answer
If the room is dry and the glass still mists, stop blaming the air. Single glazing and old frames are simply cold, and no habit changes that. Sealing draughts and upgrading glazing are the only real fixes there, and the double glazing guide covers the case where the water is inside the sealed unit.
Wipe the glass and the sill each morning in the meantime, because standing water on timber and sealant is where mould starts. If mould has appeared and covers less than about 10 square feet (roughly 1 square metre), EPA says most people can clean it themselves. Fix the water first or it returns.
Dry air and a warm pane, in that order, ends the problem
How to stop condensation on windows comes down to a short order of operations: measure, make less steam, vent what you do make, let the sun and heating reach the glass, and only then pay for a dehumidifier. Do the free things for two weeks and read the hygrometer again. In most rooms the number, and the glass, will tell you whether you are done.
FAQ
How do I stop condensation on my windows overnight?
Keep the bedroom window or trickle vent slightly open, leave the door ajar, and open the curtains by day so the glass warms up. If the room still mists, run a dehumidifier on a timer.
Does a dehumidifier stop condensation on windows?
It helps when the cause is damp air, because it lowers the humidity that feeds the water. It cannot warm a cold pane, so it will not fix single glazing or a failed seal.
Does vinegar stop condensation on windows?
Some retailers suggest a vinegar and water wipe, but I found no independent test showing it works. Treat it as unproven and fix the humidity instead.
What humidity stops condensation on windows?
Aim for 30% to 50% relative humidity, as EPA suggests, and nearer 30 to 35% in cold winter weather. The colder the glass, the lower the number needs to be.
Why do my windows get wet even with the extractor on?
The fan may be pushing steam into the house rather than outside, the door may be open, or you may be turning it off too soon. Leave it running until the mirror is clear.
