For the second cold season now, we’ve been struggling with condensation on the inside of the windows in our home. Whenever outside night temperatures fall below 10°C, the windows almost literally start to cry. This usually starts in mid-autumn and continues to mid-spring when the temperatures finally begin to rise. If you’re facing a similar issue, you’re not alone.
The physics behind this is quite simple. Air can hold moisture, and the hotter the air, the more moisture it can retain. However, when the air is cooled, the temperature drops, and the air cannot hold the moisture anymore. This causes water vapor to become liquid water, leading to condensation. In a house, this will typically happen on cold surfaces, like your cold water supply or windows. Since windows are probably the coolest surface in your house, condensation forms there the most.
In most homes, the air becomes moist for several reasons: cooking, taking hot showers, drying laundry, or even just breathing. Every time we breathe, we release moist air. A common example of this is the bathroom mirror, which fogs up after a shower. The mirror is often the coldest surface in the room, so the water vapor in the air condenses on it, making it foggy. The problem occurs when a constant damp area exists somewhere in your house, and with heating on, those damp areas can attract mold. Black mold, especially, can start to grow on windows, and it causes damage to surfaces like paint and wallpaper. It is also known to create significant health issues.
While airing out your room may reduce the moisture to some extent, it also cools down your home, and if you’re paying for heating, this feels like you’re heating up the street outside your house! You can also mop your windows, but this would require constant effort—at least two or three times a day. Alternatively, you could use chemicals to fight black mold, but again, these only address the symptoms rather than the root cause. The actual issue causing the moisture buildup is bad airflow.
Every house must have an air intake, ideally a vent in the wall. In some cases, vents on the windows or even the gap under the front door can provide sufficient airflow. Along with the intake, there should also be an exhaust. Many homes rely on a ventilation pipe that runs from the ceiling to the roof. The longer the pipe and the higher its top, the better the pressure difference, which allows for better airflow. In places like kitchens and bathrooms, an extraction fan is installed to push the air through the pipe and out of the house. However, this also results in heat loss, and you end up heating the street again. Thankfully, the heat loss is minimal, and ventilation is still essential for your home.
In some buildings and climates, even with the best ventilation system, condensation will still happen—especially on windows. Older homes, for example, often weren’t built with adequate ventilation, and even modern homes, particularly those with floor-to-ceiling windows, can face this issue. Floor-to-ceiling windows need an under-window convector heating element to direct hot air onto the glass, or the room should use air heating to avoid condensation. Even smaller windows with a radiator under them can have issues if they have a very deep window sill, blocking hot air from reaching the glass.
I struggled with mopping the windows and swearing every time I saw condensation during my first autumn and winter season, but eventually, I decided to invest in a dehumidifier. This device has made all the difference! In regions with mild winters, such as some parts of Europe and Asia, the air tends to stay humid, causing moisture to collect indoors. A dehumidifier helps by removing excess moisture in the air, preventing the condensation problem from occurring.
Dehumidifiers are essentially the opposite of humidifiers. Humidifiers are often used during winter in places with cold winters, as the air can become very dry when the temperature drops below freezing. They add moisture to the air, making it easier to breathe. A dehumidifier, on the other hand, removes excess moisture, and in my case, it completely solved the window condensation issue.
The reason I hesitated to purchase one for so long wasn’t due to the cost of the unit itself, but the running costs. Although humidifiers are relatively inexpensive, they consume electricity and need to run for extended periods to be effective. However, the dehumidifier I bought operates as a heat pump, which is a very energy-efficient technology. Heat pumps are known for transferring heat or cold more efficiently than conventional methods, meaning that for every watt of energy consumed, a heat pump can produce several times that in cooling or heating.
The process behind a dehumidifier is similar to the refrigeration cycle used in refrigerators. When air passes over the coils inside the unit, the moisture in the air condenses and is collected in a water tank. The dehumidifier works by lowering the temperature of the air inside, which causes the moisture to condense on the coils. In a similar way, air conditioners also work by removing moisture from the air, cooling the room, and preventing excess humidity.
In my case, this dehumidifier has been a miracle worker. I simply turn it on after cooking or when everyone has finished showering, and after a couple of hours, it collects the moisture from the air. I no longer have condensation on my windows, and I’ve been able to clean them and remove any mold without worrying about it returning. On laundry days, I place the dehumidifier next to my laundry, and by morning, the laundry is nearly dry, and the tank is almost full of water.
Not only does it help with moisture, but the collected water is also perfect for watering houseplants. It’s even a useful tool if you accidentally drop your phone in water! I found that placing my wet smartphone in front of the dehumidifier helps to remove the moisture from inside the device, which could prevent water damage.
If you suffer from humidity problems, I highly recommend investing in a dehumidifier. It has made a significant difference in our home, and with more powerful models available, you can find one that suits your space size and needs.