In the winter, the difference between cold outdoor air and warmer, moist indoor air can lead to foggy windows in cars and other vehicles. On a cold day, any moisture in the air inside your vehicle — from exhaling, wet clothes or snow on your boots – can lead to condensation when it hits air next to the windows that's below a certain temperature. The condensation is what makes your vehicle windows appear foggy. On a hot, humid day, the opposite happens, when the muggy air outside your car reaches the dew point against your windshield after it's cooled by your vehicle’s air conditioning.
In the winter, the difference between cold outdoor air and warmer, moist indoor air can lead to foggy windows in cars and other vehicles. Whether the fog is on the inside or the outside of your windows, it's potentially dangerous any time and can create a hazard when you can't see clearly in all directions. It’s important to know how to make sure your windows are clear — no matter the weather.
When it’s colder outside:
When the outside air is cold and you use your vehicle’s heater, fog will typically start to form on the inside of your vehicle’s windows. Here are some options to keep them clear:
- First, turn the heat on its maximum setting, because hot air can hold more moisture
- Then, if you have air conditioning, turn it on, which will pull the moisture from the air as it passes over the cooling coils
- Turn off the recirculation button so colder, dryer air is brought into the car
- If possible, crack your windows for a few minutes to help exchange the humid interior air for dryer outside air