How to stop your car windows from fogging up

Published: March 5, 2018

foggy-window Photo by wildlife_nordic/Shutterstock

Picture it. You’re in a hurry to get somewhere. You climb in the car, grateful that it’s just wet outside, and not icy. You put your seatbelt on, fire up the engine and then realize that your windows are covered in fog. You frantically wipe at your windshield, but the fog fades briefly, then comes right back. You can’t see a thing.

What do you do? And how to you stop fog from making you late again?

First, it’s a good idea to understand what’s causing your windows to steam up in the first place. Your misty windows are caused by condensation — water vapour hitting something cold and changing from a gas into a liquid. In this case, the warm, moist air inside your car is hitting windows that are colder and turning into tiny water droplets. It’s the same thing that happens to your bathroom mirror when you have a shower, or when you breathe on a window to draw a smiley face.

When you smear your sleeve or a cloth over your foggy windows, you’re not doing anything to address the moisture issue, so while you’ll have visibility briefly, the fog will come back unless you make some changes to the car’s environment.

Fortunately, there are better ways to de-mist your windows:

Run the air conditioner. This seems like a crazy idea in the dead of a cold, damp winter, but part of the AC’s job is to remove moisture from the air. If you’re not fond of the idea of blasting frigid air when you’re already cold, turn the vents away from you and turn up the heat a little. Once the windows are clear, turn the air conditioning off, you’ll save gas.

Turn up the heat. Warming up the windows to the temperature of the car’s interior will help stop condensation from forming. To prevent your driver’s side and passenger windows from fogging up, aim your vents to the side during the winter and on rainy days.

Make sure your air isn’t recirculating. You need fresh, cool air in the car to take fog away. If your air is recirculating, you’re just moving the moisture around through the system.

Open the window. Don’t do this if it’s raining, but if it isn’t, opening the windows will let the warm, moist air out of the car.

So that’s how to de-fog your car once it’s misty. But there are ways you can help keep condensation to a minimum in the first place.

Clean the inside of your windshield and the inside of your windows. Dust will give condensation more surface area to cling to, so cleaning your windows will help reduce fog. Use a windshield cleaner and a lint-free cloth (or newspaper, which lots of people swear by to get glass really clean) to make sure the inside your windshield and windows is squeaky clean. There are also products made specifically to reduce interior fogging (Rain-X Anti-Fog is one), but make sure to follow the directions carefully or you’ll end up with smears.

Shake off the water before you get in the car. Obviously, this is hard if it’s bucketing down rain, but do your best not to add to the moisture load inside the car when you get in. Shake off your umbrella or brush the snow off your jacket before you start the car up. Kick the snow off your boots as well, which you should be doing anyway, because driving with wet, slippery boots is dangerous.

Keep something moisture-absorbent in the car. A couple of socks full of (clean) kitty litter is supposed to help draw moisture out of the air and away from your windows. It may take a couple of days to start working, but will function as a basic dehumidifier after that. You can also buy cans full of absorbent silica gel, which are most often used to keep closets or electrical equipment moisture-free.  

Make sure your heaters work. If the thermostat in your car isn’t working and your heaters aren’t getting hot, it will be harder to get rid of condensation. If foggy windows are a regular problem (and you’ve tried all the other tricks), ask your mechanic to look at your heating system to ensure it’s working properly.

Check to see whether you have any leaks. If your door seals aren’t working properly, your floor mats could be getting damp and holding on to moisture, making condensation almost a sure thing. Check your floor mats to make sure they’re dry, and if they’re not, you may leaks to deal with.

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