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How to Defog Car Windows

Posted by Auto.com Staff | Jan 2, 2019

Colder weather means different things for different people. But one issue that anyone in a cold climate can expect in the winter is frozen car windows. To understand the best way to defog your car’s windows, we can start by understanding why they freeze up in the first place.

Frosty window is the result of condensation. Winter air tends to be dry because cold air can absorb less moisture than warm air. So, when you park your car at night, that moist air inside the car condenses on the windows. As temperatures drop overnight, that moisture condenses on the glass and freezes as the temperature inside the car equalizes to the temperature outside.

To avoid this, you can try putting a moisture-absorbing product in your car at night. While you can buy specific products for this purpose, there are some do-it-yourself options out there. One trick is using sock filled with cat litter on the dashboard. Oftentimes, this can be enough to absorb the extra moisture and prevent the freezing.

Cars have a defrost setting in the heating and air conditioning controls, which directs hot air at the windshield. Unfortunately, a car’s heating system requires the car to be warmed up in order to work. So when you start the car up first thing on a chilly morning you probably won’t have much luck with the defroster setting.

If you are in a hurry, and the glass is fogged up but not frozen on the outside, you can use your car’s air conditioning to defrost the windows. While it won’t be the most comfortable situation on a cold winter’s morning, the cold air blowing from the car’s vents will work to dehumidify the car with its dry air, and defog the window.

If you have an issue with ice on the outside of the window, and don’t have time in the mornings for your car’s heating system to warm up enough for the defrost setting to work, there is a tried-and-true homemade remedy that can help you out. Simply mix two parts of rubbing alcohol (isopropyl) with one part water into a spray bottle and spray on the exterior of the windshield. Rubbing alcohol won’t freeze until -138 degrees Fahrenheit, so the ice on the windshield will melt and you won’t have to worry about it refreezing a few minutes later.

It may seem counter-intuitive, but you should never use hot water to try and defrost any part of your car. Because of how water works, hot water actually freezes faster than cold water, and pouring hot water onto your car can cause it to go into small crevices where it will quickly freeze and expand, possibly breaking things.