1 year ago

How to Defog and Defrost a Car Windshield and Windows

how to defog your car windows

Every year during the winter months car owners have to deal with frosted or foggy windshields and windows. An unclear windscreen is at the top of the list of all things that can irritate a driver. In winter, when people wake up to go to work, they think less about what they’ll be having for breakfast and more about how to defog the windshield and get their vehicle ready for use. 

Once on the road, the most prominent thought in a driver’s mind is defrosting the windshield and keeping the vehicle safe to drive. This post addresses both of these questions in sheer detail, so please consider reading it to the end.

Before starting, it needs to be pointed out that the only thing more dangerous than a frosted or foggy windscreen is a chipped one. However, it is not necessary to spend thousands of dollars to get a new one. Here’s how to inexpensively repair a chipped windshield at home so that it looks as good as new.

What Causes Frost and Fog on a Windscreen in the First Place?

Whether it is a frosted windscreen or a dead car battery, the first step of solving the issue is always identifying the cause. The simple answer to this can be the cold, but having a more precise answer will help understand how to avoid these problems. 

  • Frost is caused by dew freezing on the windscreen and windows. Snowfall is obviously a reason, but windscreens can get frosted without it. Dew that settles on the windshield in the early hours of the night solidifies when the temperature falls below zero later in the night.
  • Fog on the windscreen and windows results from moisture condensing on them. It can be on both the inner and outer sides of the glass. Water vapor in the air naturally clings to any cold surface. When that happens on the windscreen, the result is a fog that blurs the driver’s vision. 

How Does a Defroster in a Car work? 

Most modern vehicles have a defrost button that can make the frost go away. As the frost is caused by low temperature, the defroster in a car heats the windscreen to remove the frost. The heating process is, however, different for the front and the rear windshields. There are three main kinds of defrosters in cars: 

Defroster Powered by the Car’s Heating System – Front Windshield 

Almost every car has air conditioning vents at the far end of the dash, just under the windshield; they defrost the windscreen. Upon turning on the defroster, the heating system of the car sends hot air to these vents. The hot air heats up the screen, and the heat helps to defrost it. 

Heating Wires Defroster – Rear Screen  

As the rear windshields of most cars do not have air conditioning vents, a different approach is used to defrost them. When the rear windshield defroster is turned on, a current passes through wires on the screen. The current causes the wires to heat up, and they heat the windshield in turn. This heat is what defrosts the rear windshield.

Gold Foil Defroster – Both Screens in High-End Cars 

In high-end cars, a very fine layer of gold is placed between the two sheets of glass that make up the windshield. The defroster in these cars works by passing a current through the gold foil, which heats up the screen and clears the frost. The gold foil is so thin that it’s transparent and serves as the electric conductor.

Don’t Have One? 

Unfortunately, if your car does not have a defroster, it’s not something that can be installed as an after-market add-on. The best approach in such a scenario would be to Trade-in or Sell the Car and get a new one that has the latest defroster tech in it.

Tips and Tricks on How to Defrost Car Windows

If it’s the morning and the car’s engine is cold, the heater won’t produce enough heat to defrost the windows. This is because it works on the hot coolant from the engine, and if the engine is cold, the vehicle has next to no heating. Here’s how to defrost the windows in such a scenario: 

Rubbing Alcohol To Defrost Windshield

One of the easiest ways to defrost a windshield is to use rubbing alcohol. All you need is a spray bottle and some isopropyl alcohol for this trick to work. Here’s how to quickly defrost a windshield: 

  1. Fill ⅓ of a spray bottle with drinking water and add an equal amount of rubbing alcohol to it.
  2. Shake the mixture well to homogenize it and spray it on the windscreen of the car.
  3. Wait for the mixture to decrease the melting point of the ice (a few minutes), and the frost will come right off. 


The concept here is the same. Salt is the most commonly used defrosting agent, from airplane wings to icy roads, and can defrost car windshields. Just sprinkle a generous amount of table salt on the windshield, and wait for a few minutes. It will decrease the melting point of the frost and clear it.

Ice Scraper 

An ice scraper, the one used to remove ice from inside a freezer, can also be used to scrape the ice off the windshield gently. This does work, but you’ll be exposing your hands to quite a bit of cold, which is not good in the winters.

Hot Water 

This last trick should only be used if no other option is available. To do this, take a bowl of lukewarm water and gently pour it on the windscreen. Be careful! If the water is too hot, it can crack the windshield. Using too much water can also have the same effect. It might be tempting to speed things up, but don’t do that. Add lukewarm water on the frozen windshield slowly and let it warm the windshield up evenly.

Tips and Tricks on How to Defog Car Windows

Fog on a car’s windows can be dangerous. It can occur in a second and completely block the view of the driver. When that happens, the first thing to do is turn on the hazard lights and slowly come to a stop. 

Consider using one of these methods to get rid of the fog: 

Turn on Max Cooling 

It might sound counterintuitive, but it works. The theory behind this is that when the car’s AC is on max cooling and air passes through the evaporator’s fins, all of the moisture is attracted to the chilled fins. Thus, the air that comes back out is completely dry. When this dry air comes in contact with the windshield, it removes the moisture from it. 

Turn on Max Heating 

Heating up the windshield will also remove the fog. To do this, set the vehicle’s heating system to maximum and direct all airflow to the windshield. The heat should clear the fog in under a minute.

Let in Fresh Air 

Fog on a windshield is mainly caused by the moisture coming from the passengers of the vehicle. The best approach to defogging the windows and windshield in such a case is to roll the windows down just a little bit and let the fresh air from outside remove the internal moisture.

Use Wipers 

The worst thing about fog on a windshield is that it is never apparent whether it is on the inside or outside of the screen. If none of the above work, the fog is probably on the outside of the car. In such a scenario, use the wipers with the windshield washer fluid. Using the washer fluid is necessary because dry wipers can scratch the screen.

Use the Defroster 

If the rear screen is foggy, turn on the defroster, and it will clear the fog from the screen in a few minutes.

How to Prevent the Screen from Fogging? 

It is next to impossible to prevent the windows of a car from frosting, but you can prevent them from fogging or at least minimize it. The thing to keep in mind is that fog occurs by water molecules clinging to the glass. If the glass can be treated to repel them, fog can be avoided. 

Some tricks that work include: 

Use a Fog Preventing Product on the Windshield 

There are fog-resistant products available on the market. Applying them on the windshield as per the instructions that come with them can significantly reduce fog on a screen.

Use Dish Soap 

If no fog-resistant products are available, dish soap can also do the trick. Apply it on the inside of the windshield and buff it into the screen. Do not wash it. This simple hack can significantly reduce the amount of fog that collects on the glass.

Do not Use Air Recirculation 

Using air recirculation in the car leads to the build-up of moisture, which condenses on the windshield. Not using air recirculation and letting fresh air in the vehicle can also decrease the chances and intensity of windshield fog.

In Conclusion

When dealing with frosted or foggy Windshields or windows, all you need to do is to keep the windows warm, one way or another, and you can prevent fog. Applying a hydrophobic coating to the windshield is also an excellent approach to solving the fogging problem. Fog and frost are, however, not the only problems for vehicles in winter. Here’s How to prep your car for winter to prevent any issues in the chilly weather. 

If your car has too many problems, making it beyond redemption, or you just feel like getting a new one, you can always Trade-in or Sell your Car.

Frequently Asked Questions 

How can I defrost my windshield quickly?

That will require a combination of all the measures taken to defrost a car’s windshield. Turn the engine on, set the car’s heating system to the max, and direct the airflow to the windshield. As the defroster heats the windshield, use a mixture of rubbing alcohol and water or concentrated salt solution to lower the melting point of the frost for speedy removal.

Do you use heat or cold to defrost the windshield?

You need to use the heating function of the car’s heat and ventilation system to defrost the windshield. Frost on a windshield is just frozen water, and you can only remove it by melting it.

How do I defrost the inside of my windshield?

It would be best if you heated it up to remove the frost. Remember that as all that frost melts, it will drip onto the dashboard and can penetrate it and cause problems. Before you set the car’s defroster to maximum heat to defrost it, please place a towel on the dash to collect the water. 

How do I defrost my windshield in cold weather?

Turn the engine on, rev it up to heat it, and turn the heater to maximum power and direct the airflow towards the windshield. 

Is it ok to use rubbing alcohol on a windshield?

Yes, it is ok to use rubbing alcohol to defrost a windshield. The only thing you need to make sure of is that it does not come in contact with the rubber seal of the windshield as that can damage/weaken it.  

What does the defroster button look like?

It shows a window with three curved arrows pointing upwards. It is usually located amidst the air conditioning controls. Some cars have a separate button for the rear windshield defroster with the same three arrow icon.

Can hot water crack a frozen windshield?

Yes, it can. As the windscreen is made of thick glass, pouring hot water on it will heat one side of the glass, and it will expand in size while the other side will remain cold. This temperature difference can cause a crack in the windshield.

Buy a used car online