Quite simply, there is moisture in your car, damp in the air, and when it gets cold in the morning, the windows are cold enough to cause the water to condensate on the windows, causing them to fog up.
On a cold day, any moisture in the air inside your car — from passengers exhaling, snow on your boots, etc. — turns to condensation when it hits air next to the windows that's below a certain temperature, called the dew point. The condensation is what makes your car's windows appear foggy.
The cause of your car windscreen misting up is actually down to water vapour in the atmosphere that occurs when your body heats the air inside the cabin – as does your breath – increasing the amount of moisture it can hold.
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.
Ventilate so the moist air leaves the house – always use the extractor fan when you're cooking, showering or bathing, leave any window vents open, and don't block off any other vents. Make sure air can circulate by leaving gaps between furniture and the wall.
Consistent build up of water on windows can lead to seals failing and water dripping through onto vital electronics and into the interior metal of your vehicle, causing rust and corrosion. Furthermore, damp interiors can destroy leatherwork, crack vinyl, encourage mould and more.
Mist often forms when warmer air over water suddenly encounters the cooler surface of land. Mist is tiny droplets of water hanging in the air. These droplets form when warmer water in the air is rapidly cooled, causing it to change from invisible gas to tiny visible water droplets.
Condensation on the outside of new windows is normal.
Condensation on the outside of new windows does not mean they are faulty. It is simply the windows doing their job of keeping your home more energy efficient.
Fog and mist differ by how far you can see through them. Fog is when you can see less than 1,000 metres away, and if you can see further than 1,000 metres, we call it mist.
Fog shows up when water vapor, or water in its gaseous form, condenses. During condensation, molecules of water vapor combine to make tiny liquid water droplets that hang in the air. You can see fog because of these tiny water droplets. Water vapor, a gas, is invisible.
The system cools the cabin by pulling humidity from the air, and that moisture needs a place to go! Technically speaking, the A/C's evaporator core condenses the humidity (turns it into a liquid). The liquid then exits the car onto the pavement via the evaporator drain. While a drip or two is normal, a puddle is not.
When the heater core is leaking, the warm coolant creates condensation inside your car when it mixes with the cold air in your cabin. This will make your windows fog up and they won't clear no matter how high you turn on the defroster. The heater core warms the air that blows through your windshield's defroster, too.
While condensation itself isn't a problem, if you do not treat it, it can cause damp patches to form where mould can grow and this can be bad for your health, as well as damaging the fabric of your home.
For the most part, a little condensation on your home's windows is nothing to worry about. It's only when you have excessive condensation on the windows, or the condensation is between the window panes that you should be concerned.
Window condensation isn't necessarily a big deal and often doesn't require attention as it generally disappears on its own. But if you're not able to easily wipe the moisture away, you might have a problem to address.
Key signs to look out for:
Weak or no airflow. Cold air (not warm) coming through the vents when the heater is on. Coolant leakage visible inside the cabin or a damp smell.
Blockage in the Condensate Drain Pipe
A warning sign that your car's condensate drain might be blocked is when you notice the water leaking inside your vehicle. If you find your car's floor getting wet with water whenever you turn your car's air conditioner on, then it's time to check your condensate drain.
Condensation is normal for properly running air conditioning systems. Excess condensation, like sweating ducts and drips from outside the unit cabinet indicates a problem with your unit and points to an HVAC system issue that requires emergency HVAC repair service.
Fog is formed when air at or near the earth's surface becomes saturated by any of the three processes - cooling, addition of moisture, or mixing with another air parcel. Generally, fog forms in a stable air mass environment.
What is the difference between Mist and Steam? Mist is water in liquid state, whereas steam is water in a gaseous state. Mist is tiny water droplets suspended in the air, whereas steam is water molecules in a high energy state; so much so that, they cannot remain together in the form of water in a bowl.
Mist forms when the relative humidity is greater than about 70%. Rain.