Should You Use Cold or Hot Air to Defog the Car?
2 Answers
Both cold and hot air can be used to defog the car. In winter, use warm air when there is fog inside the car, and in summer, use cold air. There are several reasons for windshield fogging: 1. When hot air inside the car meets the cold glass outside, condensation forms on the inside. You can open the car windows to allow air convection, speeding up air circulation inside the car and blowing away the water vapor. 2. In winter, you can direct warm air from the air conditioner toward the glass to quickly raise the glass temperature, reducing the temperature difference between the inner and outer surfaces, thereby eliminating fog. 3. During rainy summer days, you can turn on the air conditioner's cooling system to defog, activate the external circulation, and direct the airflow toward the windshield. This will create a "film of dry cold air" on the glass surface, preventing further water vapor formation. When using warm or cold air to defog, it is recommended to set the air conditioner to maximum airflow for faster fog removal.
I've dealt with foggy car windows many times before, and I used to hesitate between turning on the AC or the heater. Now I understand that using the AC defogs faster because the cold air immediately lowers the interior temperature and absorbs moisture, making the water droplets on the windows disappear quickly—ideal when you're in a hurry to drive. Using the heater also works for defogging; it evaporates the moisture to dry the glass, but it takes a few minutes to take effect while keeping the car warm. Fogging often happens on rainy days due to high humidity—don’t just wipe it with a cloth, as that’s only a temporary fix. My advice is to press the defog mode on the AC right after starting the engine; the fan can blow either cold or hot air while cracking the windows slightly or switching to external circulation to reduce incoming moisture. Regularly replacing the air filter and keeping windows clean are also crucial to prevent fogging risks. For safety, wait until the fog clears before driving—safety first.
