Should I Use Cold or Hot Air to Defog the Car?

[Rosemary]

Both cold and hot air can be used to defog the car, but cold air works faster, though it may cause fogging to reappear. Hot air removes fog more slowly, but there's no need to worry about secondary fogging. The rear windshield defogging relies on heating wires, while the front windshield cannot be equipped with heating wires, so the car's air conditioning is used to defog it. Hot air defogging requires the driver to start in advance because turning on the hot air will initially make the fog denser, affecting driving visibility. Generally, drivers should turn on the hot air defogging a few minutes before starting the car.

[OGabriel]

I usually handle window fogging based on different situations. In winter, when the car has just started and the water temperature is low, turning on the cold air defogs quickly but makes the car too cold to bear. So, I first use cold air to quickly remove the fog, then switch to warm air to maintain the effect. In humid summer conditions, I directly turn on the cold air and press the AC button for dehumidification, which works fast and effectively. Remember to activate the defogging mode to concentrate the airflow on the windshield, and the rear windshield can be defogged using the heating function. Additionally, slightly opening the windows to let in fresh air can also help reduce fogging—this is a tip from years of driving a taxi.

[DelClara]

The key to defogging lies in reducing humidity, both cold and warm air can be used depending on the situation. Cold air quickly dehumidifies via the AC compressor, suitable for emergencies or summer use, but prolonged use cools the car interior. Warm air disperses fog using engine heat, offering more comfort and lasting effect, especially useful in winter, though it requires waiting for the engine to warm up first. Regardless of the method, it's recommended to activate the AC dehumidification function and external circulation mode to let dry air into the car and prevent recurring fogging. I also prefer using rain repellent products on windows as a preventive measure to reduce fogging.

[EmilianoMarie]

My experience is that using cold air defogs the fastest. When driving and noticing fog, immediately turn on the AC button, increase the fan speed to blow directly at the windshield, and set the temperature to the lowest for the best effect—clear in just 30 seconds. It's especially effective during the rainy season in southern regions, though prolonged use of cold air increases fuel consumption. Once visibility is clear, you can reduce the fan speed and adjust to a comfortable temperature while continuing to drive. If the rearview mirror fogs up, simply press the heating button; there's no need to adjust the AC.