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How to Quickly Defog Your Car Windows

Valerie Johannsen People & Brand Manager

Every winter we face the same song and dance: fogged car windows.  While a fogged window is just condensed water, we often struggle with finding the best way to clear our windows each winter.  This week, a video has been making the rounds with the claim that an engineer has found the best way to defog car windows quickly.  He’s right, and we’ve linked his video detailing the process he used to test the right settings to defog your windshield quickly.

What Does Work

The main goal is to remove moisture from the air.  In the winter, cold air is drier because it cannot hold as much water as warm air. Once the cabin air has been dried, removing the moisture is key.

Rober, who is a former NASA engineer says these are the key items for defogging quickly:

  • Heater at Maximum
  • Defroster fan on high
  • Recirculation Off
  • Compressor (A/C) on
  • Windows slightly open

How Does it Work?

As explained in the video, using the air compressor, heating coil, and dry winter air all help to replace water-saturated indoor air with dry air, while removing moisture from the cab.

Of course, your air conditioner at home works the same way.  While it’s running, the AC unit dries out the air.  The furnace also dries out the air during the heating/cooling cycle, leaving you with very dry indoor air.  By using the compressor and pulling from the drier outdoor air, you remove water from each cycle, keep warm air in the car, and leave the excess moisture outside.

Then again, if it’s too dry in your home because of your central heating, you can always buy a humidifier.


Thank you for making Service Legends the #1 provider of residential heating and air conditioning in the Des Moines area. A live and friendly customer care representative is ready to take your call 24/7 at 515-COMFORT (515.266.3678).

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