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Condensation Risk Calculator
Find out if your windows are at risk of condensation. Enter your room conditions and window type to see your dew point, estimated glass temperature, and get tailored recommendations.
Typical humidity: Bathroom 70-90% · Kitchen 60-80% · Bedroom 50-70% · Living room 40-60%
Medium Risk
Condensation may form on your windows, especially on cold mornings.
Dew Point
12.0°C
Temperature where moisture condenses
Est. Glass Temperature
14.0°C
Inner surface of your window
Temperature Gap
+2.0°C
Glass temp minus dew point
Condensation Risk Gauge
Recommendations
Upgrading to modern double or triple glazing would significantly reduce condensation risk by keeping the inner glass surface warmer.
Installing trickle vents or an extractor fan would help remove excess moisture and improve air quality.
Avoid drying clothes indoors without ventilation. Each load of washing releases around 2 litres of water into the air.
Keep furniture away from external walls to allow air circulation and reduce cold spots where condensation can form.
What Causes Condensation on Windows?
Condensation forms when warm, moist air meets a cold surface. The air can no longer hold as much moisture, so water droplets appear on the coldest surface nearby - usually your windows.
The dew point is the temperature at which this happens. If your window's inner glass surface falls below the dew point temperature of the room air, condensation will form.
Common moisture sources
- • Cooking and boiling water
- • Showering and bathing
- • Drying clothes indoors
- • Breathing (a family of 4 produces ~8 litres/day)
- • Gas heaters without flues
How better windows help
- • Modern glazing keeps the glass surface warmer
- • Low-E coatings reflect heat back into the room
- • Warm edge spacers reduce cold bridging
- • Built-in trickle vents improve air circulation
- • Argon gas fill improves insulation
Learn More About Condensation
Struggling with Condensation?
Our experts can assess your windows and recommend the best solution to eliminate condensation in your home. Get a free, no-obligation quote.
Understanding Window Condensation: Causes, Prevention and Solutions
Condensation on windows is one of the most common problems UK homeowners face, especially during autumn and winter. Our free condensation risk calculator above uses dew point science to help you understand whether your windows are at risk and what you can do about it.
Why Do My Windows Get Wet?
Condensation occurs when warm, moisture-laden air comes into contact with a surface that is below the dew point temperature. The dew point is the temperature at which air becomes fully saturated and water vapour condenses into liquid water. Windows are typically the coldest surface in a room, making them the first place where condensation appears.
A typical family of four produces approximately 8 litres of moisture per day through breathing, cooking, showering, and other daily activities. Without adequate ventilation, this moisture has nowhere to go and settles on cold surfaces.
Did you know?
Single glazed windows have an inner glass temperature of just 9-10°C when it's 5°C outside. Modern double glazing keeps the glass at 16-17°C, and triple glazing at 18°C or above - dramatically reducing the chance of condensation.
How Different Window Types Affect Condensation
| Window Type | Est. Inner Glass Temp* | Condensation Risk |
|---|---|---|
| Single Glazed | ~9.5°C | Very High |
| Old Double Glazed (pre-2002) | ~14°C | Medium-High |
| Secondary Glazed | ~15°C | Medium |
| Modern Double Glazed | ~16.5°C | Low |
| Triple Glazed | ~18°C | Very Low |
*Based on 20°C indoor temperature and 5°C outdoor temperature (UK winter average)
How to Stop Condensation on Windows
There are two fundamental approaches to reducing condensation: lowering the moisture content of indoor air (reducing humidity) and keeping window surfaces warmer (upgrading glazing). The most effective solution combines both.
1. Improve Ventilation
- Trickle vents - Small vents built into window frames that provide continuous background ventilation without significant heat loss
- Extractor fans - Essential in kitchens and bathrooms to remove moisture at source
- MVHR systems - Mechanical Ventilation with Heat Recovery extracts stale air and recovers up to 90% of the heat
- Regular airing - Open windows for 10-15 minutes daily to exchange moist indoor air for drier outdoor air
2. Upgrade Your Windows
Modern windows are specifically designed to minimise condensation. Key features include:
- Low-E glass coatings - Reflect radiant heat back into the room, keeping the inner glass surface warmer
- Argon or krypton gas fill - Better insulation than air between the panes
- Warm edge spacer bars - Reduce cold bridging around the edges of the glazing unit
- Quality frames - uPVC and timber frames offer better thermal insulation than aluminium
Explore Our Window Solutions
Condensation Between the Panes: A Different Problem
If you see condensation between the glass panes of a double or triple glazed unit, this indicates a failed seal. The inert gas (argon or krypton) has escaped and been replaced by moist air, which then condenses when the temperature drops. This cannot be fixed with ventilation - the glazing unit needs to be replaced.
For more in-depth guidance, read our comprehensive guide: Windows and Condensation: Causes, Solutions and Prevention Tips.
Explore Our Other Free Tools
Frequently Asked Questions About Window Condensation
Why do my windows get wet in the morning?
Windows get wet in the morning because overnight temperatures drop, cooling the glass surface below the dew point of the indoor air. During the night, heating is usually off or reduced, but humidity remains from evening activities like cooking, showering, and breathing. The cold glass causes moisture in the warm indoor air to condense into water droplets. This is most common with single glazed or older double glazed windows.
Does condensation mean my windows are faulty?
Condensation on the inside of your windows does not necessarily mean they are faulty - it indicates that the glass surface is cold relative to the room humidity. However, condensation between the panes of double glazing does indicate a failed seal that needs repair or replacement. Modern double and triple glazed windows with Low-E coatings significantly reduce internal condensation because they keep the inner glass surface warmer.
What humidity level should I keep my home at?
The ideal indoor relative humidity is between 40% and 60%. Below 40% can cause dry skin, irritated eyes, and respiratory discomfort. Above 60% increases the risk of condensation, mould growth, and dust mites. In kitchens and bathrooms, humidity may temporarily rise to 70-90% during cooking or showering, which is why good extraction is essential in these rooms.
Will new double glazing stop condensation completely?
Modern double glazing with Low-E coating and argon gas fill significantly reduces condensation by keeping the inner glass surface around 16-17°C compared to just 9-10°C for single glazing. While it will not eliminate condensation in extremely humid conditions, it dramatically reduces the risk. Combining new windows with adequate ventilation (trickle vents, extractor fans) is the most effective approach.
What is the dew point and why does it matter for windows?
The dew point is the temperature at which air becomes saturated and water vapour begins to condense into liquid water. For windows, if the inner glass surface temperature falls below the dew point of the room air, condensation will form. For example, at 20°C with 60% humidity, the dew point is approximately 12°C. If your window glass is colder than 12°C, you will see condensation.
Is condensation on windows bad for my health?
Persistent condensation can lead to mould growth around windows and on walls, which can trigger asthma, allergies, and respiratory infections. Black mould (Stachybotrys) is particularly harmful. The NHS recommends keeping homes well ventilated and addressing condensation promptly. Upgrading to modern windows and improving ventilation are the most effective long-term solutions.
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