How to Stop Window Condensation

Do you wake up in the morning to find your bedroom windows covered in condensation?

It’s certainly not the best way to start the day. Unfortunately, many of us experience pools of water on our windowsills and black mould around the frames, especially in the colder months.

This is a common problem in the UK, but it doesn't have to be. Stopping it is easier than you might think.

The first part of our guide deals with the causes, providing useful insights, but you can jump straight to our tips on reducing window condensation.

• What causes window condensation?
• Is condensation on windows a problem?
• Preventing condensation on a window
• Ventilation systems for reducing condensation on windows

What causes window condensation?

When warm, moist air comes into contact with a cold window, it releases moisture onto the glass as water droplets. This is window condensation.

There is a precise point when condensation occurs, which is known as the dew point. This is reached when the air is cooled to a specific temperature, at which point it releases water. The colder the window, the easier it is for the dew point to be met. You’ll often find condensation forming initially at the bottom and edges of windows, as these are the coldest areas.

Windows are impermeable, which means liquid can’t travel through them. So when water settles on them, there’s nowhere for the moisture to escape to. But where does this water vapour in the air come from? Everyday activities like cooking, showering and drying clothes all generate moisture.

Why is there more condensation overnight and in the morning?

Condensation is normally most noticeable, or only present, on windows in the morning. There are a few reasons why this is the case.

The main reason is that the temperature difference between inside and outside increases overnight. Your windows are normally the coldest surface in your house and the most likely surface to reach the dew point.

When you close your curtains at night, you’re effectively stopping the internal heat from directly heating your windows. This makes them a colder surface again. You’re also less likely to have windows open at night, so any created moisture can’t escape.

In the case of bedrooms, you generate moisture from breathing while sleeping, increasing the humidity of the room. This is a perfect recipe for overnight condensation that you’ll see on your windows in the morning.

Condensation on windows in winter

At Permagard, we receive hundreds of calls from people wanting to know how to stop condensation on their windows in winter.

During the winter months, you’re more likely to have the heating on, which warms the air in your home. Warm air holds more moisture than cold air, so humidity is higher. You’re also less likely to open windows in the winter, so the moist air can’t escape. The surface temperature of your windows will also be much lower.

Together, this means there’s more moisture in your home that will be deposited more easily onto windows. The colder the night, the more condensation you’re likely to experience.

Is condensation on windows a problem?

Wiping down your windows every morning is annoying, but is it actually a problem? Beyond the inconvenience, there are more serious issues to understand.

Small amounts of condensation are normal and shouldn’t cause any major problems, however, excessive condensation is more of a concern.

It can lead to black mould growth on and around your windows. Mould is a fungus that needs moisture for its spores to grow. The main concern with black mould is the health risks, as it can exacerbate existing conditions. It is a bigger concern in bedrooms, as you could breathe in spores throughout the night.

Condensation and mould can also damage your internal decoration, and you may need to repaint or re-wallpaper problem areas. Excessive condensation will also damage your windowsills and even your window units.

If you’re getting lots of condensation on the internal side of your windows, then there’s a chance that you’ll also be getting condensation in other areas of your home that are less visible. This can lead to further instances of black mould and potentially more significant structural damage.

Condensation between windowpanes

Condensation on the inside of double-glazed windows suggests that the units have failed. There’s likely to be a fault in the seals that has allowed some moisture to get between the two panes of glass and form condensation. You are likely to require new windows to resolve this issue.

Should you wipe condensation off windows?

You should wipe condensation off windows. Moisture allows mould and mildew to grow, and leaving condensation can create an environment where these can thrive. It will also prevent damage to window frames and sills.

Preventing condensation on windows

Solutions range from small practical changes to installing a passive vent or a whole house ventilation system. And yes, we’ve heard all the weird and wonderful solutions here at Permagard: from washing up liquid to condensation catchers to miracle sprays. Our focus is on practical, logical behaviour changes and proven ventilation solutions.

Our Top Tips

Practical

1. Cover pans when cooking and use an extractor fan if you have one
2. Don’t dry your clothes indoors
3. Take shorter showers with doors closed and windows open when possible
4. Open windows and doors to ensure good ventilation throughout the house, ideally at opposite sides of your house to aid cross-ventilation
5. Ensure your house maintains a warm temperature
6. Open trickle vents on double-glazed windows

Longer-term solutions

1. Kill any mould with a mould wash
2. Apply an anti mould paint to stop mould growth from coming back
3. Ensure there is no underlying damp issue
4. Install a ventilation system that matches your needs - we offer an overview in the next section to help you select the right ventilation option.

How to stop condensation on windows overnight

You might find more condensation in the morning because temperatures drop overnight, and, in winter, you might be less likely to use the heating overnight. It’s also likely to be more apparent in bedrooms where people have been breathing throughout the night. We look at some room- and season-specific advice below, but essentially, if you’re reducing condensation in the daytime, then there should be less moisture in the air to condense overnight.

How to stop condensation on windows in winter

Opening windows is not such a viable option in winter, and you’re less likely to be able to dry clothes outdoors. Ensure rooms where you dry washing indoors are well-ventilated, or use a tumble dryer. Make sure you’re keeping the house warm. Warm air is better able to hold moisture, so less will be deposited as condensation. Also, try to open windows for short bursts in the morning to let humid air escape.

How to stop condensation on bedroom windows

Bedroom windows can be prone to condensation because you will be creating additional moisture in the air throughout the night from breathing. Ensuring there’s some form of ventilation, whether that’s an open door or window or installing a ventilation system, will help. Keep the room reasonably warm, and you can even look at getting thinner curtains to allow more heat from the room to reach the window.

If you have condensation problems in your bathroom, then read our guide to avoiding condensation and treating mould in your bathroom.

Ventilation systems for reducing condensation on windows

The best option for getting rid of condensation permanently is installing a ventilation system in your home.

Positive input ventilation

Positive input ventilation, or PIV systems, work by continuously replacing the moist air in your home with fresh, filtered air from outside. They are usually installed in your loft and provide whole-house ventilation.

They’re quiet, cheap to run and effective. In many homes, condensation can be reduced significantly within a few days of installation.

Permagard stocks Nuaire Positive Input Ventilation systems that offer PIV for houses with lofts, 3-storey buildings and ventilation units for flats without a loft space. There are also options for models that heat the incoming fresh air.

Read our guide for a more in-depth look at the pros and cons of positive input ventilation.

Heat recovery systems

Heat Recovery ventilation systems work by drawing out moist air in your home and replacing it with filtered, fresh air from outside. They include a heat exchange unit that captures the heat from the air leaving your home and uses it to warm the incoming fresh air. This significantly reduces the amount of heat wasted and reduces your energy bills.

The Kair Heat Recovery Ventilation Unit recovers up to 86% of heat from outgoing air. This makes it a highly effective solution to condensation in a single problem room. Click for more information about installing a Kair unit.

Passive ventilation

Passive ventilation, like our Perma-vent, uses natural forces to encourage airflow through your property. These vents contain no moving parts, making them very affordable and easy to maintain. They are easy and quick to install yourself and will start working straight away.

Window Trickle Vents and Condensation

Many modern double-glazed window units feature trickle vents. These vents are located at the top of the window as part of the frame and allow air from outside to enter your home at a low rate. They represent a form of background ventilation that works on the passive ventilation principle.

Trickle vents won’t completely solve the issue, but they will help with ventilation and reduce condensation. It’s important to note that trickle vents cannot be retrofitted, so if your double-glazed windows don’t feature them, you’d need to get new ones installed. You’ll also need to consider other forms of ventilation to work alongside them.

Dehumidifiers for window condensation

Dehumidifiers can be effective at removing moisture from the air in single rooms and damp rooms, but they aren’t necessarily a long-term or energy-efficient solution. These units can help reduce humidity around specific activities, such as cooking and if you need to dry clothes indoors.

Dehumidifiers are less practical for reducing the issue across your home. If the humidity is high throughout the house, you would require quite a few powerful dehumidifiers to reduce the moisture enough to stop condensation. A much more cost-effective option is PIV, which removes humid air and replaces it with fresh, drier air - a much wiser long-term investment.

Permagard – Over 35 Years of Experience in Condensation Control

You should now have a good idea of the best ventilation methods to stop window condensation. Browse our full range of condensation control products to find the right solution for your home. The NHS also has a page on preventing condensation and mould.