How to defog your car windows quickly
Last updated: March 2023
No matter what the climate is like where you live, keeping the temperature comfortable inside your car may mean battling foggy windows. If you live in a climate with cold winters, you're often using the heater to stay warm in your car, which can result in fog on the inside of your windows. In warm, humid areas, turning on the air conditioning (AC) can cause the opposite issue — fog blurring your windows from the outside. To reduce or eliminate the fog or condensation, you should try to adjust the temperature on the inside of the car to match the outside temperature as closely as possible.
The reason for foggy windows has to do with temperature and the air's moisture content. 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. 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 AC system.
Whether the fog is on the inside or the outside of your windows, any time you can't see clearly in all directions, it's potentially dangerous. So, it's important to know how to make sure your windows are clear — no matter the weather.
When it's colder outside than inside your car...
When you're dealing with cold weather outside and you turn on the heater inside your car, the fog typically will start to form on the inside of your car windows. Here are some options to defog those windows:
For a quick fix: According to Road and Track, this is the fastest way to defog your windshield:
- First, turn the heat on its maximum setting because hot air can hold more moisture.
- Then, turn the AC on, which will pull the moisture from the air as it passes over the cooling coils.
- Finally, turn off the recirculation button so colder, dryer air is brought into the car.
- If possible, crack your windows for a couple minutes to help exchange the humid interior air for dryer outside air.
For a more comfortable solution: Lifehacker advises those who want to be snug and warm while driving to turn on the defroster and blow warm air across the windshield to evaporate the accumulating moisture. If your vehicle's ventilation system has a recirculate feature, turn it off. When this feature is on, your car's heat or AC reuses the air inside the car instead of continually pulling in air from outside.
If you're trying to defog the windows in cold weather, you want your car to continually take in the drier outside air instead of reusing the more humid air inside the vehicle. (Not sure if your car has recirculation? Look for a button on the dashboard that has an arrow going in a circle or a semi-circle. Sometimes, it will feature an icon of a car with this type of arrow inside it.)
When it's warmer outside than in your car...
When the temperature and moisture level outside are greater than inside the car, moisture will condense on the exterior of the car glass. Similar to when it's colder outside than the inside of your car, the goal is to change the temperature on the inside of the car to match the outside temperature.
In this case, it means warming up the inside. Keep the following tips in mind:
- First thing: Use your windshield wipers. This will help get rid of the condensation until you've balanced out the temperature.
- Warm up your car: Turn down the AC to the lowest (least-cool) setting to increase the temperature without it becoming too uncomfortable. If this doesn't work, turn the AC off completely, says Lifehacker.
- Leave recirculation off: As stated above, it's a good idea to turn off your car's recirculation feature to battle foggy windows so the temperature and moisture levels in your car begin to equalize with those outside.
Trying to see through fogged-up windows can be a driving hazard, but with these tips, you can help increase your driving safety — no matter the weather.