How to fix condensation inside a car

All vehicles can be affected by condensation inside the car. To explain why this happens and how you can lessen or prevent it, we’ve prepared these helpful suggestions.

Condensation explained

Humidity in the air causes condensation inside the car. When warm, humid air inside the car meets a cold surface, such as the inside of your car’s windows when it’s cold outside, the moisture in the humid air cools and condenses on the cold surface.

The condensed moisture forms into hundreds of tiny droplets of water. Depending on the humidity of the air inside the car, this may look like a fog across the windows. It can even create noticeable drops of water when there’s a lot of moisture present.

Causes of condensation

Several factors can increase the humidity inside the car and contribute to condensation forming:

• Wet shoes, clothes, umbrellas – even pets! When it’s wet outside and you get into your car, moisture on your garments, shoes and other items evaporates into the air as they dry. Carpets and seats can also absorb water from your shoes and clothes which later dry as the moisture evaporates into the air.
• Breath – every time you breathe, you exhale water vapour in your breath. The longer you and your occupants are in the car, the more moisture you breathe into the cabin.
• Water ingress – ageing or damaged seals can sometimes allow water into the car.
• No circulation of fresh air – the longer the air remains in the car, the more humid it can become.

Condensation inside new cars

Modern cars have better seals and better insulation than older cars. Better seals mean that new cars are more water- and air-tight, making it harder for humid air inside the car to escape to the outside. Therefore, it’s important to introduce fresh air into the car, exchanging the humid air and lowering moisture levels.

Better insulation in modern cars means they stay warmer for longer when parked. The longer there is a difference between the warm cabin temperature inside and the cooler air temperature outside, the more condensation can form on the inside of the cold windows.

How to fix condensation inside the car

The key to reducing condensation inside the car is lowering the humidity level of the cabin air. Venting the humid air to the outside can prevent the condensation from coming back or even getting worse.

The best way to remove the moist air is to use the car’s air conditioning system. Part of the air conditioning is designed to cool the air, causing the moisture to condense. The air conditioning system collects this condensation and drains it outside the car.

Another technique is to set your climate control to ‘outside’ or ‘fresh air’ rather than ‘recirculate’ mode. Regularly introducing fresh air from outside will replace the humid air in the cabin, lowering moisture and condensation.

You can also use the demister function to quickly clear the windscreen and side windows of condensation. By blowing air over the windows, the moisture evaporates, effectively drying and clearing the windows. The demister function in many cars turns on air conditioning by default, recovering evaporated moisture and draining it through the air conditioning system.

Using your car’s heating and air conditioning system as suggested will lower humidity and moisture levels inside the car, helping to lessen condensation forming. However, it is unlikely to prevent it entirely – if it’s cold enough outside, any residual moisture in the cabin air will find its way to the cool surface.

Keeping the inside of your windows clean, especially the windscreen, can also help. The cleaner the glass, the less likely condensation will form and the more effective the demisters will be in clearing any condensation that does appear.

If damaged or ageing seals are allowing water into the car, replace the damaged seals as soon as possible. Your local Lexus centre can help identify the source of any leaks and carry out the necessary repair work.

Lastly, buying a car dehumidifier bag can help with persistent condensation. These small bags contain silica gel or other moisture-absorbing granules that act as passive dehumidifiers. They continuously extract moisture from the air, and many are reusable – dry them out and pop them back in your car as required.