Using Cold or Warm Air to Defog in Winter?

[BriannaFitz]

In winter, use warm air to defog. Here's more information: 1. Turn on the warm air, but defogging takes time. After turning on the warm air inside the car, the temperature difference between the inside and outside of the car will become greater, and the fog will become heavier. Once the temperature inside the car rises, the moisture in the air decreases, and the surface temperature of the windshield gradually increases, the fog will naturally dissipate. 2. Precautions for defogging with warm air. Defogging with warm air requires the driver to act in advance because turning on the warm air will make the fog heavier for a short time, affecting driving visibility. The driver should turn on the warm air to defog a few minutes before driving.

[VonLukas]

I've encountered the issue of windshield fogging up several times during winter driving. Turning on the cold air defogger works quickly because it rapidly lowers the glass temperature and reduces condensation, but it makes the car interior extremely cold, significantly affecting comfort especially during long-distance driving. Using warm air, although slower (fog appears first then gradually disappears), maintains a warm cabin and is more suitable for winter use. My personal recommendation is to directly use warm air and set the AC to defog mode - most vehicles have a dedicated button with a small fan icon. This automatically adjusts air vents and activates the compressor for dehumidification, achieving both quick defogging and energy efficiency while avoiding prolonged cold air exposure that might cause colds. Preventing fogging can be achieved by reducing interior humidity - avoid bringing wet items into the car or crack open a window slightly for ventilation. I noticed more frequent fogging after installing a car humidifier, but the situation improved significantly after removing it, with the key benefit being safer driving with clear visibility.

[PenelopeDella]

As an experienced driver, safety is always the top priority. In winter, turning on the heater is the preferred method for defogging, but it's not enough to just activate the heater. You should also enable the defrost function, usually marked with a defogging symbol. This will start the air conditioning compressor to assist in dehumidification, preventing water accumulation on the glass that could impair visibility. Fogging occurs due to temperature differences and moisture condensation. While cold air can dehumidify quickly, it may make the interior uncomfortably cold, especially for the elderly and children. Gradually heating the glass with warm air to disperse the fog is more reliable. After starting the vehicle, preemptively turn on the heater at a low fan speed a few minutes in advance to prevent fogging—this is more effective than dealing with it afterward. I always keep a dry towel in my car to wipe away minor fogging. Developing this habit has significantly reduced major issues, making driving safer and lowering the risk of rear-end collisions.

[VanLeah]

I found that using the cold air for dehumidification in winter is indeed effective for defogging, but the chill is too uncomfortable for passengers. It's more recommended to use warm air combined with the defogging mode of the AC. Many cars can activate this with just one button, automatically directing airflow to the windshield for quick defogging without the cold. After the engine warms up, using warm air consumes almost no extra energy, whereas cold air wastes fuel by running the AC compressor. Remember to adjust the temperature moderately—keep it below 26°C. Avoid using recirculation mode when fogging occurs to prevent moisture buildup. Simple preventive measures like keeping the AC filter clean and the windshield clear are enough. With good maintenance, my car rarely fogs up.

[OAndres]

In winter, I prefer using the heater to defog. It gradually warms the glass, reducing moisture condensation with high comfort. However, it requires operating the high-speed defogging mode, which is easily done with just a button press—no hassle. Using cold air works instantly but makes you shiver from the cold and is less eco-friendly, wasting fuel due to higher AC energy consumption. Large temperature differences easily cause fogging, especially in rain or snow. It's advisable to warm up the engine before driving for more effective defogging. Placing a moisture-absorbing defogging bag on the dashboard can also help. My car has automatic climate control—once the temperature is set, the system adjusts itself, making it very convenient. Keeping a clear view is crucial for safety. Don’t forget to regularly check the heating system to prevent blockages that could affect defogging efficiency.