What to Do When Fogging Occurs with Heater On?

[StHeidi]

Turning on the heater can help defog the windows. Additionally, you can switch the air conditioning to external circulation mode and adjust the vents to defog mode, which will prevent the car interior from getting too cold. After the front windshield fogs up, roll down the window slightly to allow outside air to circulate inside the car, which will quickly disperse the fog. Keep a towel handy to wipe away fog when it appears. Applying a mixture of dish soap or soapy water, then rinsing with clean water and drying, can prevent fogging for a short period. Glycerin can also be used for this purpose.

[DeNadia]

The most effective way is to directly turn on the defogging mode of the air conditioning, don't worry about that little bit of fuel. After the car warms up, press the front windshield defogging button (the one with the fan-shaped symbol), and the air conditioning will automatically switch to external circulation with increased fan speed, dispersing the fog in two minutes. I usually turn the temperature to the highest first, wait until the glass is thoroughly heated, and then lower it by a degree or two, which helps prevent the fog from recurring. If the rear window has electric heating wires, remember to turn them on, especially useful on rainy days. Make sure to turn off the internal circulation, otherwise, the breath will be trapped inside the car. By the way, if fogging up frequently, keep a chamois cloth handy for emergency glass wiping, but never wipe while driving—it's too dangerous.

[Ortiz]

I found that window fogging mainly occurs because the glass is too cold, and when the warm, humid air inside the car condenses on it, it forms water droplets. The solution requires a two-pronged approach: after starting the car, don't rush to turn on the heater. First, roll down all the windows for about a minute to ventilate and equalize the temperature inside and outside. When using the heater, keep the temperature below 25°C, set the fan speed to medium or higher, and direct the vents toward the windshield. The most crucial step is to turn on the A/C button—don’t think using the air conditioning is silly, as the compressor’s dehumidification efficiency is ten times higher than the heater. Household anti-fog sprays also work well; just spray them on the inner side of the windows during car washing, and they’ll keep fog away for a week.

[LeBeau]

I often use a zero-cost DIY method: cut a raw potato in half and vigorously rub it on the inside of the glass. After it dries naturally, the starch film formed can prevent fogging. If you notice fogging while driving, don't panic—immediately open diagonal windows with a 2-3 cm gap for ventilation, and turn the heater to maximum to blow on the glass. When parking, remember to place a dry towel on the windshield to absorb evaporated moisture from the interior. If the rearview mirror fogs up, you can use soapy water to wipe the lens as an emergency solution. Budget-conscious drivers can also purchase an anti-fog sticker for around ten yuan, which works well when applied to the inside.