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Buying Guide

Condensation on Bedroom Windows — Why It Happens and How to Fix It

Updated July 2026

Bedroom windows are the worst in the house for condensation. Every morning, dripping glass, wet sills, damp curtains. If you don't fix it, black mould follows within weeks. The cause is simple: you breathe out a litre of moisture overnight, the heating is off so the room cools, and the cold window glass collects all that moisture. Here's how to fix it — from free tips to products that solve it permanently.

Quick answer

Our top pick: Devola 12L Dehumidifier

£85 – £110 on Amazon

The 3 fixes in order: 1) Open the bedroom door at night (FREE — reduces condensation by around 30%). 2) Place absorber strips along the window base (£6). 3) Run a dehumidifier set to 50% RH (£85–£200 — the permanent fix).

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Why bedroom windows get condensation

Three things stack up overnight to make the bedroom the worst room in the house:

  • Breathing. A sleeping adult exhales around 1 litre of water vapour into the air over 8 hours. Two people = 2 litres. That moisture has to go somewhere.
  • Cold windows. Bedrooms usually have the coldest glass in the house because the heating is off for the longest. Warm, humid air hits the cold pane and drops its moisture on contact — that's condensation.
  • Closed room. Bedroom doors are closed at night. The moisture you produce can't escape into the rest of the house, so it concentrates around the coldest surface: the window.

6 fixes — from free to permanent

  1. Open the bedroom door at night — FREE. Lets moisture disperse across the rest of the house instead of concentrating on the coldest window. Reduces condensation by around 30% on its own.
  2. Leave a curtain gap — FREE. Closed curtains trap cold air against the glass. A 10cm gap at each side lets warm room air reach the pane and keeps it above the dew point.
  3. Absorber strips — £6. Sit along the window base and soak up the overnight moisture before it pools. Check on Amazon →
  4. Anti-fog spray — £10. Coats the glass so moisture beads and runs off rather than fogging the pane. Check on Amazon →
  5. Window insulation film — £15. Adds an insulating air layer that raises the inside pane temperature — warmer glass, less condensation. Check on Amazon →
  6. Dehumidifier — £85–£110. The permanent fix. Set to 50% RH and the machine cycles on and off overnight, keeping bedroom humidity below the condensation threshold. Check on Amazon →

Full overnight condensation guide →

All bedroom condensation products compared →

Is bedroom condensation dangerous?

Condensation on its own is not dangerous — it's just water on glass. The danger is what it enables. Persistent condensation soaks into window frames, sills and the wall behind curtains, creating the damp surface black mould needs to colonise. Once mould appears, spores enter the air you're breathing all night.

Long-term exposure to mould spores can trigger asthma, allergic reactions and respiratory infections — the risk is highest for children, older adults and anyone with existing lung conditions. Keeping bedroom humidity below 60% RH prevents mould from establishing in the first place. See target humidity levels for UK homes →

Bedroom condensation in rented flats

Landlords often blame condensation on the tenant's "lifestyle" — drying washing indoors, cooking with lids off, not opening windows. But the underlying issue is usually the building: no trickle vents, single glazing, cold external walls, no working extractor fans. If you've tried the fixes above and still get condensation every morning, the problem is structural.

Under Awaab's Law your landlord must investigate reported damp within 14 days and act on hazards within a strict timeframe. Photograph the condensation and any mould, log the dates and report in writing. Read your rights under Awaab's Law →

Which fix do you actually need?

Start with the two free fixes tonight. If condensation is still forming in the morning, add absorber strips. If your window still drips despite both, you have enough moisture in the room to need a dehumidifier — nothing else will keep up.

How to choose the right fix

Tip

Try the two free fixes first

Open the bedroom door at night and leave a small curtain gap. If your condensation is mild, that alone can stop it — no products needed.

We recommend

One dehumidifier ends the problem

For persistent, dripping-every-morning condensation, a proper 10–12L compressor dehumidifier set to 50% RH ends the problem permanently. Running cost is around 5–8p per hour and it only cycles on when needed.

Warning

Don't ignore black spots on the sill

Small black dots on the window frame or sealant are early-stage mould. Clean them off within a week and fix the underlying humidity — leaving them lets the colony spread into the wall behind the curtain.

Frequently asked questions

Bundle

The Bedroom Condensation Fix Kit — Approx. £120

Total:approx. £126
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