Condensation on windows is common, especially in autumn and winter. However, condensation does not always mean that there is something wrong with your glass. Where the condensation is located determines what is going on. Condensation on the inside usually indicates too much moisture and too little ventilation in the house. Condensation on the outside is often a sign that your glass is insulating properly. Condensation between the glass plates usually means that your insulating glass is leaking and needs to be replaced.
In this article we explain how to recognize the difference, what causes it and what you can do about it.
Why does condensation form on glass?
Condensation occurs when warm, moist air cools against a cold surface. Glass is sensitive to this, because windows are often colder than the air in the house. The more moisture there is in the air, the faster condensation forms. Consider moisture by:
- cooking
- shower
- laundry drying
- breathe
- plants
- poor ventilation
- insufficient heating
- cold bridges around window frames
As soon as that moist air hits a cold window, water vapor turns into small droplets. You see that as fogged up glass.
The location of the condensation determines the problem
Not all condensation is the same. Therefore, first check carefully where the moisture is.
| Where is the condensation? | What does it usually mean? | What can you do? |
|---|---|---|
| Inside of the window | Too much moisture in the house | Better ventilation |
| Exterior of the window | Glass insulates well | Usually do nothing |
| Between the glass plates | Insulating glass is leaking | Replace window |
| Around the frame | Cold bridge or ventilation problem | Check frame/ventilation |
So the most important question is: can you touch the condensation?
Can you wipe away the condensation? If the moisture is on the inside or outside, you can wipe it away and it is usually a ventilation or weather problem. If it is between the glass plates and the haze remains visible, you cannot reach it and your window is probably leaking.
Condensation on the inside of the window
Condensation on the inside is on the living side of the window. You often see this in bedrooms, bathrooms and kitchens. The cause is usually a combination of:
- high humidity
- cold windows
- little ventilation
- insufficient air circulation
- temperature differences between inside and outside
Especially with single glazing and old double glazing, condensation quickly forms on the inside. These windows remain colder on the inside, causing moisture to precipitate more quickly.
Is condensation on the inside a problem?
A little condensation is not immediately a big problem. Do you occasionally see it in the bedroom in the morning? This is often due to moisture from breathing during the night. But wet windows every day are a warning sign. Too much moisture in the home can cause:
- mold on walls and window frames
- wood rot
- peeling paint
- stale air
- dust mites
- health problems
- black spots around windows
Does water often remain on the windowsill? Then you need to improve ventilation.
What can you do about condensation on the inside?
The solution is usually: better ventilation and reducing moisture. Practical tips:
- open ventilation grilles
- open windows briefly every day
- use extraction when cooking and showering
- dry laundry preferably outside or with good drainage
- heat rooms evenly
- do not place furniture tightly against cold outside walls
- dry wet windows
- check whether ventilation grilles are clean
Ventilating does not mean that you have to open windows all day. Kort en krachtig luchten werkt vaak al goed, zeker als er daarna voldoende basisventilatie blijft via ventilatieroosters of mechanische ventilatie.
Does HR++ glass help prevent condensation on the inside?
Yes, often. HR++ glass keeps the inner glass plate warmer than single glazing or old double glazing. This means that condensation is less likely to form on the inside. You can easily put together HR++ insulating glass in the right size yourself.
But HR++ glass does not automatically solve every moisture problem. If the humidity in your home remains too high, condensation can still form in cold places. That is why the combination is important:
- better insulating glass
- sufficient ventilation
- good heating
- healthy humidity
New glass without ventilation can cause new problems. A home is better insulated, but moisture must still be able to escape.
Condensation on the outside of the window
Condensation on the outside is on the outside of the glass. You mainly see this with good insulating glass such as HR++ glass, triple glass and vacuum glass. This often happens:
- early in the morning
- in the autumn
- on clear nights
- with high humidity outside
- when there is little wind
Many people think there is something wrong with the glass, but usually the opposite is true.
Why is condensation on the outside a good sign?
With well-insulating glass, the heat stays inside. The outer glass plate therefore becomes relatively cold. When moist outside air hits that cold outside window, condensation is formed. This means that the heat from your home does not simply escape through the glass.
Condensation on the outside is therefore often a sign that the glass is working properly. You mainly see this with:
- HR++ glass
- triple glass
- vacuum glass
- modern insulating glass with coating
Do you need to do something against condensation on the outside?
Usually not. Condensation on the outside will disappear automatically as soon as:
- the outside temperature rises
- the sun hits the window
- the air becomes drier
- there is more wind
You can of course wipe the window clean, but technically that is not necessary. Do you want to reduce the effect? Then an overhang, sun blinds or better air flow around the window can help. But in most cases, condensation on the outside is not a problem.
Condensation between the glass plates
Condensation between the glass plates is a problem. You see this with double glazing or insulating glass when the edge seal is leaking. You recognize it by:
- moisture between the windows
- a white or gray haze
- drops in the cavity
- chalky spots
- dirt that you cannot brush away
- fogged glass that does not disappear
The most important feature: you can't reach it. You clean the inside and outside, but the haze remains visible.
How does leaking insulating glass occur?
Insulating glass consists of several panes of glass with a closed cavity between them. This cavity usually contains dry air or noble gas. The edge seal keeps moisture out and gas in. Over time, that seal can fail due to:
- old age
- poor placement
- tension in the glass
- damage to the edge
- bad sealant edges
- moisture load
- operation of the frame
- production errors
If the seal develops a leak, moist outside air enters the cavity. Condensation then forms between the glass plates.
Can you repair leaking double glazing?
Not good in practice. You cannot reliably "refill" or permanently dry a leaking window. There is sometimes talk online about drilling holes or removing moisture, but that is not a sustainable solution for insulating glass.
If there is condensation between the glass plates, the insulating effect is affected. The best solution is to replace the window. You can then immediately opt for better insulating glass, such as:
- HR++ glass
- triple glass
- vacuum glass
- laminated insulating glass
- insulating glass with ventilation grille
How can you be sure that your window is leaking?
Use this simple check:
- Clean the inside of the window.
- Clean the outside of the window.
- See if the haze, drips or spots remain.
- Check whether moisture is visible in the cavity.
- See if the problem keeps recurring.
Does the haze remain visible while both glass surfaces are clean? Then the problem is probably between the glass plates.
| Complaint | Probable cause |
|---|---|
| Moisture can be wiped away on the inside | Condensation inside |
| Moisture can be wiped away on the outside | Condensation outside |
| Haze remains after brushing | Leaking insulating glass |
| Drops visible in cavity | Leaking insulating glass |
| Only wet at the bottom of the frame | Ventilation or cold bridge problem |
When should you replace glass?
You do not have to replace glass immediately if there is condensation on the inside or outside. You can usually solve this with ventilation or let it disappear on its own. Replacement is wise when:
- there is condensation between the glass plates
- the glass is permanently hazy
- your insulating glass is leaking
- the window is old double glazing
- you lose a lot of heat
- you still want to become more sustainable
- the sealant edges are bad
- the frame is renovated
A leaky window is not just ugly. The insulation value is also considerably worse. As a result, you lose more heat than necessary. Use the U-value calculator to calculate how much better new insulating glass performs. Are you unsure whether new glass will fit in your existing frame? Then read thicker insulating glass in an existing frame.
Condensation and ventilation grilles
Ventilation grilles can help to reduce moisture problems in the home. Constant ventilation is important, especially in well-insulated homes. A ventilation grille provides fresh air without having to keep opening a window. A grid is especially useful in:
- bedrooms
- living rooms
- kitchens
- bathrooms with window
- areas where condensation often occurs
Are you having glass replaced? Then that is a good time to immediately see whether a ventilation grille is needed. The grid is then included in the dimensions of the glass.
Condensation on new glass: is that normal?
Yes, sometimes. After installing new HR++ glass, condensation on the outside may occur more often. This usually means that the new glass insulates better than the old glass.
The indoor climate can also change. Old cracks and bad glass inadvertently provided ventilation. After installing new insulating glass, the house is more dense. This means you have to ventilate more consciously. New glass sometimes requires new ventilation habits.
Common mistakes with condensation on windows
- Thinking that all condensation means glass problems. Interior condensation is usually a ventilation problem. Condensation on the outside is often a good sign.
- Trying to clean a leaky window. You cannot wipe away condensation between the glass panes. You simply can't reach it.
- Installing new windows without ventilation. Better insulation without ventilation can cause moisture problems. Therefore, also consider grilles or a ventilation system.
- Only look at the glass. Moisture problems can also be caused by cold bridges, window frames, walls, poor extraction or too much moisture production in the house.
- Waiting too long before replacing leaking glass. Leaking insulating glass loses insulation value. Replacing prevents heat loss and improves visibility.
Preventing condensation: practical checklist
- Ventilate daily.
- Use extraction when cooking and showering.
- Leave ventilation grilles open.
- Dry wet windows.
- Keep interior doors open sometimes for air circulation.
- Heat rooms evenly.
- Check sealant seams and window frames.
- Replace leaking insulating glass.
- Consider HR++ glass for old single or double glazing.
- Install ventilation grilles with new glazing.
Conclusion
Condensation on windows is not always bad. The location of the condensation determines what is going on. Condensation on the inside usually means that there is too much moisture in the house and that you need better ventilation. Condensation on the outside often occurs with well-insulating glass and is usually not a problem. Condensation between the glass panes indicates leaking insulating glass and means that the window needs to be replaced.
So first take a good look at where the moisture is. Can you wipe it away? Then it is usually a ventilation or weather problem. Is it between the glass plates and does the haze remain visible? Then your window is probably leaking.
Do you want to know more? Read how to measure glass to size or what the difference is between toughened and laminated glass.
Do you want to replace a leaking window or better insulate immediately? Then choose new HR++ glass, triple glass or vacuum glass and immediately consider a ventilation grille. Customize your glass and easily order online.