When it’s cold outside, foggy windows are a common occurrence, even in covered parking. They can affect your driving vision and safety. But how does it happen?
In a nutshell, windows fog up because the temperature outside is cooler than the air temperature inside the vehicle.
Air trapped in a vehicle is usually warmer and more humid than the cold air outside. Windows and windscreens are usually cool from the outside temperatures so as the warmer air gets in contact with the cool glass, the inside air temperature drops and so does its capacity to hold moisture, the result ends in water vapour (fog) on the inside of the windscreen and windows.
That all happens when there’s nobody in the vehicle, so when people are inside the car, breath and body temperature further increases the humidity.
Should I use hot air or cold air to clear my windows?
Turn on the air conditioning and blast cold air to the windscreen. Using hot air usually clears the windscreen temporally because it evaporates the water vapour however after a few minutes, it actually makes the situation worse as it pumps more humid air inside the vehicle.
It’s tough when the mornings are cold, however once the cold air has been circulated, inside air humidity will lower. After this, turning up the temperature slowly will give keep you warm from the outside elements.
Don't forget NRMA Members get 20% off window repairs and replacement with National Windscreens.