Defog Your Car Windshield Like a Pro This Winter: Here Is How

The winter is knocking on the doorstep. Car owners take many steps to ensure that their prized possession is ready to tackle the worst of the cold season. However, there’s one issue that plagues every driver daily during the winter months – windshield fogging. 

Despite a rapid evolution in vehicular technologies, manufacturers are yet to figure out a failproof solution to windshield fogging. No cutting-edge AI-based electronic system or innovations in glass material have managed to solve the 'mist-i-fying' issue for almost a century now! 

Humans, hence, have relied on workarounds for over a century to keep their car windshields from fogging up while doing triple-digit speeds on expressways. A majority of drivers and cab operators rely on the old-school method of wiping away the condensation with a piece of cloth (or by their palms if a cloth isn’t readily available) but that affects visibility by creating vision distortion, especially at night when oncoming vehicles cast their headlights on high beams. 

However, highly experienced drivers and automotive experts have a few clever tips to share for defogging a car’s windshield during the freezing winter months of North India. 

In this story, we are going to explore some of the common reasons that lead to windshield fogging and how you use some clever tricks to defog the glass for a safe driving experience. 

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Why do car windshields fog up in winter?

The magical concept of windshield fogging is totally dependent on the basic laws of thermodynamics. The fog you see on the glass is condensation which happens primarily from the humidity present in the cabin. The humidity mostly emerges from breath and other wet articles.  

During the winter season, the cold air outside reduces the temperature of your car’s exterior panels, including the windshield and all other glass surfaces. Once you get in and start driving, the car’s heater along with your moist breath makes the cabin air humid, which tends to amplify the warmth. The warmer air inside the cabin also warms up the windshield and all other glass panels.

However, the windshield now experiences a drastic difference in temperature on either side. The cold air outside causes a greater cooling effect and thanks to the laws of thermodynamics, the hot air inside starts to condense. The tiny droplets depositing on the walls of the windshield are what you perceive as fogging on the glass.

In layman's English, the phenomenon is similar to a cold bottle of water condensating in the summer months. Hot air blowing outside deposits moisture on the cold surface of the bottle.

Coming back to your car's windshield, while you can wipe away the fog temporarily with a piece of cloth, the humid cabin continues to deposit condensation on the inside of the windshield. 

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Methods to defog your windshield cleverly 

While wiping your windshield seems to be an easier short-term solution, it only makes visibility worse. Hence, here are some other clever tricks to defog your car’s windshield with a longer-lasting effect. 

Adjust the cabin temperature

One way to fight the fog on your windscreen is to bring down the cabin temperature significantly. This process reduces the humidity in the cabin and therefore, drops the levels of condensation on the glass. You can use your vehicle’s AC with minor cooling to address the fogging. 

Turn on the Demist/Defrost Mode

But what if the temperature outside requires the HVAC system of your car to keep the insides warm? You can turn to the Demist/Defrost mode. 

Almost all cars today feature a demist fan setting on the AC fan controls. Refer to the buyer’s guide from the manufacturer and find out how you can turn on the Demist Mode. 

When enabled, it blows cold air through the vents angled at the insides of the windshield. The higher the fan speed, the quicker the defogging happens. However, you still need to turn down the cabin temperature to achieve the desired clarity on your windshield. 

Switch off the HVAC circulation 

The air circulation mode is effective when you need to keep your car’s cabin cold and dust-free in the summer months. However, during winters, recirculating the humid and warm air through the vents leads to fogged-up windshields. Hence, it is recommended that you turn off cabin recirculation when the glass fogs up. Once the colder fresh air starts flowing in, the humidity in the cabin drops immediately and visibility improves. Most modern cars can keep the cabin heated up while the recirculation is turned off. 

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Avoid turning on the heater before starting your vehicle 

If you are venturing out with up to two or three layers of warm clothes on a moderately cold day, try to avoid using the heater system. The cabin may feel cold but once you get used to the temperature, you can drive longer without the glass fogging up. With no cabin heating, the humidity inside the cabin stays under control, thus preventing condensation. 

Roll down your windows slightly

Another way to keep the cabin humidity in check is by rolling down the windows slightly to let fresh dry air in without freezing you and your passengers. This way, you continue to enjoy the warmth of the heater system without letting it fog up. 

Use homemade chemical solutions for temporary relief

Most drivers rely on household chemical solution to defog their car’s windscreen. Many recommend applying soap solution to the inside of the windshield and wiping it off. Some suggest creating a solution of one part vinegar and two parts water and spraying on the inside of the glass. Some have even recommended applying a shaving cream solution on the inside and wiping it off to prevent fogging. 

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Frequently Asked Questions (FAQs)

• Why does my car’s windshield fog up even with the defroster on?
  The defrost mechanism may not work efficiently if the cabin is too warm and humid. Try turning off the re-circulation mode of your HVAC system.
  
  
• Can I use household products to prevent fogging?
  Some recommend using common household commodities like soap, vinegar-water mixture and shaving cream to defog the insides of the windshield. 
  
  
• How do I prevent windshield fog when driving in winter?
  You can reduce the temperature of the cabin, allow for fresh air flow by rolling down windows and turning off air re-circulation, turn on the demister/defogger mode for the windshield and apply chemical solutions.