Should You Use Cold or Hot Air to Defog the Car Interior?

[SanIan]

Use cold air to defog the car interior. Here is an introduction to car fogging and defogging: Reason for using cold air: When fog forms on the front windshield of the car, you can use cold air to defog it. This is because the fog inside the car is caused by hot air inside the vehicle meeting the low temperature of the front windshield, forming water vapor that adheres to the windshield. At this point, simply turning on the car's cold air can eliminate the fog. This cold air can be directly applied using the external circulation to blow on the front windshield. If the effect is not satisfactory, you can also use the air conditioning's cooling mode to blow on the front windshield, which will quickly eliminate the condensation of hot and cold air on the windshield. Detailed process for car defogging: If you want to completely eliminate fog inside the car, you should choose to turn on the air conditioning and use hot air to blow on the windshield. Similarly, start with the external circulation, select the hot air mode and the front windshield outlet, wait for about 5 minutes, and then switch to internal circulation or simply turn it off. Of course, if the air conditioning has a heating function, the defogging effect will be faster and better.

[MatthewLee]

When there's fog inside the car, I always turn on the heater first to deal with it, because experience tells me this is the most effective method. Fog forms due to the temperature difference between the inside and outside of the car, causing moisture to condense on the cold glass. The hot air quickly heats up the interior air, evaporating the moisture, which clears the fog fast and safely. Remember to turn on the air conditioning's external circulation mode to let dry air enter the car, avoiding the use of internal circulation alone, which can worsen the fog. Although cold air can dehumidify and cool in the summer heat, it tends to make the fog denser initially, which is not conducive to driving. In daily driving, especially during rainy days or winter, heavy fog can obstruct vision and affect driving safety. Therefore, I regularly check the air conditioning system to ensure the filters are clean and unclogged. By handling the fog properly once, the next drive becomes much easier, and after forming this habit, I've almost never encountered heavy fog again.

[AnthonyDella]

When there's fog inside the car, my suggestion is to turn on the heater. This is based on physics: warm air increases the humidity capacity, allowing the fog to evaporate, which is especially suitable for cold weather. In practice, I prefer to follow a sequence: after starting the vehicle, directly set the air conditioner to heating mode and aim the airflow at the windshield; if the fog persists, switch to the defrost function for assistance. In hot summer days, cold air can be tried for dehumidification and cooling, but don't turn it on immediately to avoid worsening condensation. For safety, keep a low speed or pull over when defogging, and avoid distracted driving. I also often remind myself to open the window slightly to balance the pressure, which can prevent fog from forming too quickly. Regularly cleaning the windows and air vents also helps a lot—after all, prevention is better than cure.

[VanIker]

When encountering fog inside the car, I would choose to turn on the hot air to quickly clear it. Fog is the result of water vapor condensation, and hot air can heat the air to evaporate moisture, making it more reliable than cold air. The operation is simple: start the air conditioning, set it to the warm air setting, and blow directly onto the glass—it usually takes effect within seconds. Cold air can be tried for dehumidification in hot weather, but it is less efficient. In terms of safety, fog obscuring vision is very dangerous, so after defogging, ensure the road is clear before driving. I also recommend occasionally using the external circulation mode to bring in fresh air to maintain dryness. Simple maintenance, such as cleaning the glass surface with an anti-fog coating, can reduce recurrence.