How To Defog A Windscreen
Overview
Why does my windscreen fog up?
Your windscreen fogs up because of condensation. This occurs when the glass is cooler than the surrounding air. In winter when the air inside your car is significantly warmer than the glass, fogging will occur on the inside. In summer, with the air conditioning on; the reverse happens and windscreen fogging can occur on the outside. This is less common because the movement of outside air typically dries the condensation before it can build up. Fogging occurs even more readily when there’s excess moisture in the air during rain or particularly humid days. Now let’s look at some defogging windscreen tips.
How to stop your windscreen from fogging up?
The first step to stop your windscreen from fogging up is to keep it clean, inside and out. Dirt attracts moisture. You can also try using an Antifog windscreen treatment or interior glass treatment. If it’s a cold or rainy day and your windscreen has fogged up on the inside, switch your fan to demist mode with your air conditioner in recirculate mode. This will dehumidify the air in the cabin. Cracking a window can also help by equalising the interior and exterior air temperatures. If the fogging is occurring on the windscreen during a humid summer day, just flicking the wipers on will help and once you’re moving; the increased air speed should clear it up. Switching off your air conditioner and opening the windows will also help.
Steps
Use your wipers
If the fog is on the outside of the windows, running your wipers will clear it up. Once you get on the road, the moving air will prevent the fog from condensing.
Run the engine
The sooner you can get the engine warmed up, the sooner your heater will operate. And running the heater is the key to clearing fog inside your windscreen. In an electric car the heater functions almost instantly.
Set your ventilation
Ensure your fan is drawing fresh air rather than recirculating, switch your ventilation to defrost mode, and turn the air conditioner on. The air conditioner will dry the air and help to clear up the fog until your heater takes over.
Open a window
If you can’t wait for the heater to kick in and you can handle the cold wind for a moment, opening a window works especially well to shift the warm, moist air out of your car.
Wipe the fog
If you really can’t see and you need to get a move on, keep a microfibre towel handy to wipe the fog from the windows. However, you will find that the fog returns quickly if you haven’t employed any of the previous steps.
Tweak your ventilation
Once the heater is working at its best, the fogging will clear up SUPER quick. After a while you may find yourself getting too hot and you can turn the heat down. If the fogging then returns, try running the air conditioner to dry the air alongside the heater.
Tips & FAQs
What is the fastest way to defog a windscreen?
The fastest way to defog a windscreen depends whether the fog is on the inside or the
outside of the window. On the outside, getting on the road is the fastest way to defog a windscreen. Or
using your windscreen wipers of course.
If the fog is on the inside, running the air conditioner and the heater simultaneously on full blast will
quickly defog your windscreen. Unless your heater isn’t up to temperature, then opening the windows is
often the best.
Should I use hot or cold air to defrost my windshield?
Hot air is always the best choice to defog a windscreen. This is because hot air can hold more moisture than cold air, meaning it won’t condense to form fog on your windscreen. Further to that, heating the glass will minimise the temperature difference between the inside and the outside of the windscreen, which helps to further reduce condensation.
How do I defrost my car windows?
You can defrost your car windows using the heater, which will gently heat the glass to melt the frost. Because frost is on the outside of the windows, this will take longer than defogging. If the frost is thin, your windscreen wipers may help, and manually scraping the frost away is of course very quick. Just ensure you’re using a scraper which won’t damage the glass.
How to defog your windshield when it’s raining?
Rain will cause windscreen fogging to be especially bad because of all the excess moisture in the air. The colder the rainy day, the worse it will be. Once you’ve hopped into the car, potentially with damp clothes and a wet umbrella – the problem is exacerbated. To defog your windscreen when it’s raining, you’ll usually need to set both the air conditioner and heater to maximum to combat the humidity.
*Important information* - Click here to read more about our How-To terms and conditions.