A close-up view of a heart drawn into the condensation on a car’s rear windscreen.
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The best ways to de-fog your windows this winter

Should you use the air conditioning or fan? And should the temperature be warm or cool? Here’s the best way to clear foggy windows in cold weather.

By Shell on Jun. 14, 2022

It’s one of the less pleasant aspects of winter driving. Just when it’s cold, foggy or pelting down and you really need to see where you’re going, your car makes the whole job harder by fogging up on the inside.

More than just annoying, a car with fogged-up windows can be downright dangerous. But while you can’t control the weather, you can ensure your vision isn’t compromised when you need it. Here’s how.

Keep your glass clean

Beyond smear marks, dog slobber and other obvious vision inhibitors, your car’s inner glass gets coated in a light oily haze over time due to airborne contaminants that develop from the cabin plastics, vinyls and other materials.

While your car’s heating, ventilation and air-conditioning (HVAC) system is typically capable of defogging even hazy glass, it’ll do it a lot quicker if the glass is clean because clean glass is harder for water vapour to attach to – in short, your windows won’t get so foggy.

How to clean it? There are any number of retail windscreen polishes or glass cleaners that will do the job but a damp chamois towel and some elbow grease can also be effective.

Let your HVAC system do the work

Depending on your car, you’ll have one of two styles of HVAC systems to play with – automatic, otherwise known as ‘climate control’, or manual. Both have everything needed to defog your windows and keep them clear; you just need to know how to use them.

1. Manual HVAC
The cause of fogged-up windows is a combination of excess moisture in the cabin air and the glass being colder than that air, causing condensation on the inner surface. The solution is giving it a blast of hot, dry air. To do this, switch your air-distribution mode to ‘windscreen’, then flick on your air-conditioning (a/c) – while that might seem counterintuitive in cold weather, it will bring the air-moisture level down. Next, switch off your air-recirculation mode. This will allow the HVAC system to bring in some drier outside air rather than recirculating the moisture-laden cabin air, further lowering the air-moisture content. Finally, crank your temperature to full hot (hotter air absorbs more moisture), ramp up your fan speed to full and flick the rear-screen demist button. Your windows should steadily transform from foggy to crystal-clear.

2. Climate control
If you’ve got the fancier kind of HVAC setup, you’re in luck – simply activate the system’s automatic demist/defog function (look for a standalone button with a windscreen symbol) and let it do the work for you. This function sets the climate control up for optimum defogging by essentially emulating the process outlined above, all at the touch of a button.

Maintaining clear vision

Driving along with the fan speed and temperature set to max can be a bit much, so how do you maintain comfort without bringing the fog on again?

The key is keeping the a/c on – this will keep a tab on the air moisture – and that drier air blowing on the glass, so use ‘feet/windscreen’ mode if you must spread the warmth rather than removing the airflow from the windscreen altogether.

Once the glass is clear, you should also be able to keep it that way with reduced fan speed and temperature. If things start fogging up again, a bit of finessing of those two settings should help you maintain the desired balance of comfort and clear vision.

Disclaimer

Viva Energy Australia Pty Ltd (“Viva Energy”) has compiled the above article for your general information and to use as a general reference. Whilst all reasonable care has been taken by Viva Energy in compiling this article, Viva Energy does not warrant or represent that the information in the article is free from errors or omissions or is suitable for your intended use.