Should You Use Cold or Hot Air to Defog Car Windows in Winter?
4 Answers
In winter, hot air should be used to defog car windows. When using hot air for defogging, adjust the temperature to a higher setting, increase the fan speed, and use the external air circulation to expel moisture from the vehicle. Methods to solve window fogging include: 1. Turn on the front window defogging mode, increase the fan speed, turn on the temperature control, and lower the temperature; 2. Activate the one-touch defogging function; 3. Open the windows to increase air circulation, reduce the temperature difference inside and outside the car, and weaken the conditions for fog formation; 4. Spray defogging agent evenly on the glass surface and wipe it clean with a dry towel; 5. Make a DIY defogging solution using dish soap and apply it before driving.
Just helped my mom with this headache a couple of days ago. While the warm air conditioning in winter is comfortable, blowing it directly onto the windshield actually makes the fog form faster because the moisture from your breath condenses on the cold glass. I usually just turn on the A/C button to cool—the air conditioning compressor can actually remove moisture from the car. Pair it with the defrost setting and blast the air at the windshield. It’ll feel a bit cold at first, but hold out for about ten seconds, and the fog will clear. Then you can turn off the A/C and switch back to warm air if you want. For foggy side mirrors, spraying some anti-fog solution in advance can keep them clear for three or four days. And remember—never wipe the windshield while driving, it’s dangerous!
As a driver with ten years of experience in Northeast China, I've tested and proven that hot air is the real deal. When starting the car, first open the windows to disperse the fog. Once the water temperature gauge rises a bit, turn directly to the defrost setting + hot air + external circulation. The first five minutes might get foggier—don't panic! The hot air warms up the glass, and the moisture naturally stops sticking. This method works flawlessly for long drives and keeps your feet warm. Adding 75% alcohol to the windshield washer fluid can help in emergency defogging. If the temperature difference between inside and outside the car doesn't exceed 5°C the night before, placing a dry towel on the dashboard can also absorb moisture.
I heard from a car mechanic about the fundamental principle: fogging occurs when warm, humid air inside the car hits the cold glass and condenses into water droplets. So theoretically, cold air dehumidifies the fastest. When I drive an electric car, I just tell the voice assistant to activate the automatic defogging, and the compressor clears the view in thirty seconds. But at minus ten degrees, the cold air blowing on my arms is unbearable. Later, I discovered a clever trick: set the air conditioning to 24 degrees with low fan speed, and press the windshield and front window heating buttons simultaneously. This is like using warm air to 'insulate' the glass, preventing fogging almost entirely. Remember to replace the air filter regularly; a dirty filter cuts the defogging effect in half.
