Condensation on windows is a common problem in UK homes, especially during colder months when warm, moist air hits cold glass. Left unchecked, it can lead to mould, damp walls, and damage to window frames. This guide explains the ten most effective ways to stop window condensation, ranked by practicality and cost.
The most effective way to stop condensation on windows is to reduce indoor humidity by using extractor fans in kitchens and bathrooms, and by opening trickle vents on modern double-glazed units. Without controlling moisture at source, no window upgrade or treatment will permanently solve the problem.
What matters when you choose: Condensation on windows is caused by warm, moist air meeting a cold surface. The fix is always about reducing humidity or raising the glass temperature, not about “curing” the window itself. Your choice depends on your budget, whether you rent or own, and how much ventilation you can tolerate, especially during winter.
| Method | Typical cost (GBP) | Effectiveness | Lifespan |
|---|---|---|---|
| Extractor fan (installed) | 150–400 | High | 10–15 years |
| Dehumidifier (portable) | 80–250 | Moderate | 3–5 years |
| Trickle vents (retrofit) | 50–150 per window | Moderate | Indefinite |
| Window film (secondary glazing) | 20–80 per window | Low–moderate | 1–3 years |
| Wiping down windows | 0 | Low (temporary) | Ongoing |
| Keeping furniture away from walls | 0 | Low–moderate | Ongoing |
| Avoid drying clothes indoors | 0 | Moderate | Ongoing |
| Draught-proofing strips | 10–30 per window | Low–moderate | 3–5 years |
| A-rated double glazing | 2,000–5,000 (whole house) | High | 20–25 years |
| Moisture-absorbing products | 5–15 per pack | Low (temporary) | 1–3 months |
1. Run extractor fans during and after showers
This is the single most effective step you can take. A bathroom extractor fan removes moisture-laden air directly outside before it spreads through your home. Running it for 20 minutes after a shower removes up to 90% of the moisture generated (Energy Saving Trust, 2026).
- Install a fan with a humidistat so it runs automatically when humidity exceeds 60% (GOV.UK Part F, 2026).
- Also run the kitchen extractor fan whenever you cook, especially when boiling water or using a hob.
- For best results, leave the bathroom door closed while the fan is running to stop moist air escaping into other rooms.
2. Open trickle vents on double-glazed windows
Trickle vents are small slots built into the top of modern window frames. They provide continuous background ventilation without creating a noticeable draught. Keeping them open 24/7 reduces indoor humidity by 10–15% in winter (Energy Saving Trust, 2026).
- Trickle vents are required by building regulations on all new and replacement windows (FENSA guidance, 2026).
- If your windows lack trickle vents, a glazier can retrofit them for £50–150 per window.
- Do not block trickle vents with curtains or blinds, they need clear airflow to work.
How to improve home ventilation without losing heat
3. Use a portable dehumidifier in high-moisture rooms
A portable dehumidifier is a good option if you cannot install extractor fans or if condensation persists despite good ventilation. A 10–20 litre/day model can extract 1–2 litres of water per day in a typical home (Energy Saving Trust, 2026). Running it costs roughly 10–15p per hour based on the 2026 average electricity price (Ofgem, 2026).
- Place the dehumidifier in the room where condensation is worst, usually the bathroom or kitchen.
- Set it to maintain humidity below 60%, this prevents condensation forming on any cold surface.
- Empty the water tank daily; some models have a continuous drain hose for permanent use.
4. Wipe down windows each morning
This is the simplest temporary fix. Wiping condensation off glass every morning prevents water from pooling on sills and seeping into frames, which can cause mould and rot (GOV.UK damp guidance, 2026).
- Use a microfibre cloth, do not let water sit on timber or uPVC frames (FENSA maintenance advice, 2026).
- Wring out the cloth into a bucket, not onto the floor or sill.
- If you have timber windows, dry the frame thoroughly to prevent the wood from swelling or rotting.
5. Keep furniture away from external walls and windows
Furniture pushed against external walls or directly under windows blocks airflow, trapping moisture against cold surfaces. A gap of at least 10cm behind sofas and wardrobes allows air to circulate (Energy Saving Trust, 2026).
- Move beds and wardrobes away from external walls by at least 10cm.
- Avoid placing large furniture directly in front of radiators, this stops warm air reaching the window.
- Check behind furniture regularly for signs of mould or damp.
6. Avoid drying clothes indoors on radiators
Drying a single load of washing indoors releases 2 litres of moisture into the air (Energy Saving Trust, 2026). This moisture then condenses on cold windows and walls, causing persistent damp problems.
- Use a vented tumble dryer or dry clothes in a separate room with the door closed and window open (GOV.UK, 2026).
- If you must dry indoors, place the drying rack in a room with an extractor fan running.
- Consider a heated airer with a cover, it still releases moisture but at a slower rate than a radiator.
Best ways to dry clothes indoors without causing damp
7. Install secondary glazing film on single-glazed windows
Secondary glazing film is a low-cost option for homes with single glazing. A low-E (low emissivity) film can raise the internal glass temperature by 3–5°C (Energy Saving Trust, 2026). This keeps the inner pane above the dew point, reducing condensation.
- Apply the film to the inside of the window frame using double-sided tape, then shrink it with a hairdryer.
- Low-E film is more effective than standard clear film because it reflects heat back into the room.
- Secondary glazing film lasts 1–3 years before it needs replacing (GOV.UK, 2026).
8. Check and seal window frames for draughts
Draughty windows let cold air in, cooling the glass further and making condensation more likely. Draught-proofing strips cost £10–30 per window and stop cold air cooling the glass (GOV.UK, 2026).
- Fit self-adhesive foam strips or metal brush strips around opening casements.
- Do not seal trickle vents, they are needed for ventilation (FENSA, 2026).
- Check for gaps around the frame where it meets the wall; fill these with sealant if needed.
9. Replace old single glazing with A-rated double glazing
This is the most expensive option but the most effective long-term solution. A-rated double glazing has a U-value of 1.2 W/m²K or lower, compared to 5.0 for single glazing (GOV.UK, 2026). This keeps the inner pane warmer and reduces condensation by up to 60% (Energy Saving Trust, 2026).
- Look for windows with a BFRC rating of A or above.
- Triple glazing is not necessary for condensation control, A-rated double glazing is sufficient.
- Replacement windows must comply with building regulations, including trickle vent requirements.
Double glazing U-values explained what rating you need
10. Use a moisture-absorbing product near problem windows
Moisture absorbers containing silica gel or calcium chloride crystals can trap 0.5–1 litre of moisture per month (Energy Saving Trust, 2026). These are a temporary fix, not a replacement for ventilation or extraction (GOV.UK, 2026).
- Place absorbers on windowsills in rooms where condensation is persistent.
- Replace the crystals or empty the water reservoir every 4–6 weeks.
- Use these only as a stopgap while you address the underlying moisture source.
Controlling indoor moisture is the only permanent way to stop window condensation. Start with the free and low-cost steps, running extractor fans, opening trickle vents, and avoiding indoor clothes drying, before investing in dehumidifiers or new glazing.
Frequently Asked Questions
Condensation on windows is caused by warm, moist air hitting a cold glass surface. According to the Energy Saving Trust, reducing indoor humidity with extractor fans or dehumidifiers is the most effective fix.
Yes, opening windows for 10-15 minutes a day can reduce humidity by up to 30%. The Energy Saving Trust says this is a low-cost method, but it may not be practical in winter.
A portable dehumidifier costs around £30-£60 per year to run, based on 8 hours daily use (Energy Saving Trust). It's a moderate-cost solution that lasts 3-5 years.
Yes, A-rated double glazing keeps the inner pane warmer, reducing condensation by up to 50% compared to single glazing. According to the Glass and Glazing Federation, it also cuts heat loss by 30%.
Trickle vents are small slots in window frames that allow background airflow. They cost £50-£150 per window to retrofit and reduce condensation by improving ventilation, as recommended by GOV.UK Part F.
