Why does the inside of a car fog up?
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Jan 27, 2015  |  Vote 0    0

Why does the inside of a car fog up?


How many times, especially since temperatures are about the only things heading south these days, have you climbed into your car on a cold day and, after starting the vehicle, had the windows fog up?

With a little patience and some foresight, you can address this problem like a champ and be the envy of friends, family and neighbours in no time.

First of all, it’s important to understand where this fog comes from.

Simply, windows fog up when warm, moist air in the car meets colder glass surfaces, causing condensation.

Humidity levels inside a car can increase just from passengers breathing, clothes that are wet from rain, a smelly damp gym or equipment bag, snow that people drag in on their boots, damp floor mats and – the classic example, think back to those heady, hormone-infused evenings while in high school.  Even hot take-out food elevates moisture levels.

When the inside windows fog up, turn on the defrosters (front and rear) and crank up the heat. The air conditioning (if available) comes on automatically when the windshield defroster is turned on in most current vehicles; that will dehumidify the air and clear windows faster.

Remember, warm air contains more moisture, but it's the relative humidity that matters. Warm, dry air coming through the defroster will clear the glass faster than cool air. In fact, it's best to use fresh air instead of the recirculation mode since the latter will recycle the moist air that was the cause of the problem.

So now you know how to deal with it when it’s there. It can be minimized, even prevented. Those stinky gym bags and a wet umbrella? Banish them to the trunk. Snow on your boots? Knock it off as best you can before you swing your legs inside. You know the importance of keeping the outside of your car free from dirt, salt and grime. Consider cleaning the inside of all windows on a regular basis; dirt gives moisture a base to settle, making it easier for fog to form.

But wait; there’s more! This does work! Clean interior window surfaces as before, then slice a clean potato in half. Rub the cut surface of the tuber on the windshield, covering all areas. The results, if done properly, will astound you!

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