As the Velvet Underground song goes, “I got a foggy notion!” … but, I confess, when it comes to fogged up windows, I don’t have the foggiest. Having full understanding on how to stay safe when your windows mist up is essential driver knowledge. There are always things to learn in the automotive world, and there’s nothing more dangerous, and frankly, terrifying than hurtling down the motorway when your windows start to fog up.
So, why do car windows fog up when you’re driving and what can you do to avoid it – or just stop it – as soon as it happens?
How window fog occurs
When a thin mist layers on the inside of a car’s glass, this is known as window fog.
When a car’s windows are cooler than the dewpoint temperature, fog occurs. What’s the dewpoint temperature you ask? That’s the temperature at which the atmosphere must be chilled to reach saturation, with saturation equalling 100 percent relative humidity. Condensation happens when the air temperature falls below the dewpoint.
So, to get rid of condensation, you need to reduce moisture from the car.
How to prevent window fog
Luckily for you, there’s bound to be an easy fix to your fog issue. Below we’ll cover off the main ones we know of, but do some experimentation (always safely, of course) to figure out what your vehicle likes best.
Clean the window
Water particles attach to dust and pollutants on the window more easily. Fog will be lessened if the windows are clean.
Check for leaks
Check for water leaks in your car. Fogging is more likely when there is a lot of moisture inside the automobile.
Try using an anti-fog product
There are a few products on the market that apply a coating to the window to reduce fogging.
Get rid of excess water
Remove any extra water and avoid bringing it into the automobile. If you can avoid it, don’t bring wet clothes or umbrellas into the car when it’s raining. If you have the opportunity, toss them in the boot.
This might sound silly, but they do actually make car dehumidifiers. These can be placed under the windscreen to remove moisture. You could even go as far as keeping some baking soda or kitty litter in the car!
Have a vent
Recirculate the air. Vents should be open and it’s a good idea to also crack a window before parking to allow the car to release any humid air.
How to remove window fog
Pump the air conditioning
It’s not just for hot days that air conditioning (A/C) is used. Use it if you have it, liberally! The goal is to remove moisture, so crank up the air conditioning.
Use your heater
If you don’t want to freeze with the air conditioning on, turn on the heater and direct heat to the windows, which will warm them over the dewpoint.
Try a demister cloth
Keep a demister cloth in your car to wipe the rain off the windscreen. A whiteboard eraser, according to some, is an excellent tool for removing fog. Whatever suits your needs. Make sure you’re not dirtying-up the windscreen by employing a contaminant-causing item. Also, keep in mind that safety comes first, so pull over to the side of the road before attempting to clear the windscreen.
Recirculate the air
Make sure that the recirculation vents are open to enable fresh air in and damp air out.
Is your car’s air condition and heater working tickety-boo? If not, have it checked by a My Auto Shop mechanic to get it operating efficiently to help prevent the fog!