Car Tech

Foggy Windows, and How to Stop Them Fast

You know when you finish your morning shower, and you go to check your fine self out in the mirror, and you can’t see diddly-squat because of the fog? Or, when you can see your breath in the morning, so you know the day will be cold and miserable, and you start to wonder why you don’t live in Miami?

Both of these types of fog are the same type that proliferate in various thicknesses and intensities on your vehicle’s glass and body, which can be an annoyance, with the potential to be dangerous.

Foggy windows aren’t too complicated, but they’re a little complicated. Is your knowledge of fog a little hazy? This is something we mist address. So – full steam ahead for the deal on foggy windows, and how to deal with them fast.

Here’s what you need to know.

What’s in the air?

The air we breathe has many characteristics, including temperature and moisture content. In the context of foggy windows, air exists at a certain temperature, and it contains a certain amount of moisture, which can be a little or a lot. Remember this.

What is the dew point?

At a specific temperature, moisture in the air can be released, turning into dew or frost. Sciencey folk call this process condensation, which is a thing that occurs at something called the dew point – which is the temperature at which water in the air condenses into droplets that collect on things and stuff.

When you see droplets all over your lawn, or a layer of frost covering your windshield, you’re seeing the results of condensation. Basically, when conditions are right, humidity in the air condenses onto cool surfaces, like your gladiolas, your windshield, or even particles in the air (which is how clouds are formed). Science!

Several factors are at play, but here it is in a nutshell: when humid air touches something cool, that humidity condenses and leaves moisture behind in the form of fog.

Exterior car window fog

If it’s muggier than a leather blanket outside, and you’re blasting the bejesus out of your ride’s air conditioner, the vehicle windows are cooler than the air outside. Humid outside air touches the exterior of your glass, and the moisture condenses onto them. This is less likely if the vehicle is moving, or if it’s exposed to the sun. Simple solution here: use your wipers.

Another? Turn off you’re a/C to heat the glass up, remembering that condensation has trouble forming on warmer surfaces – but who wants to do that when its super-gross hot out?

Interior car window fog

Your car’s interior windows fog up when warm and humid air from inside contacts the cool windows, causing the moisture to condense into that annoying fog. Add more humidity to the air, or lower the temperature of the glass, and there’s more fog to be had.

Clearing up interior car window fog

To reduce or eliminate interior window fog, you need to eliminate one or both of the conditions that cause it, by reducing the level of humidity, or increasing the temperature of the windows, or both.

So, turn on your defroster, and pump some warm, dry air over the glass. Remember, when you heat the glass up, you make it much harder for condensation to take place. Further, the air flow from the climate control system will typically push the humid air out of the car.

Fun fact: humid air can be pushed out of your car, even when your windows and doors are all closed, because your car has hidden vents that allow for this.

Foggy windows and A/C

In most cars, the air conditioning turns itself on when you turn on the windshield defroster.

“But it’s winter! Why on earth would the A/C turn on? I’m turning it off – this is stupid, clearly something is wrong with my car,” say many drivers.

Thing is, your air conditioner both cools and dehumidifies your vehicle’s cabin. When you dehumidify the cabin, you reduce the amount of moisture in the air that’s available to turn into fog.

Translation? Leave the A/C on, and the heat on, in the defroster setting. Don’t have A/C? Just focus on getting as much hot dry air onto the glass as possible.

Another option is to roll down your windows, to bring the temperature of your windshield and cabin closer to the temperature outside of your car, while letting some of the hot and humid air mass escape quickly.

Pro tip

Check your owner’s manual for info on the climate control “recirculation” function, and make sure it’s off when your windows are foggy. This forces drier air into your ride, and forces more humid, fog-causing air out.

Tips to prevent interior window fog

To keep interior window fog at bay, reduce moisture sources inside of your ride. Wet floor mats, a box full of steaming take-out pad thai, multiple cups of tea, or even your carpool passenger who never seems to stop talking, are all pumping humidity into your cabin.

Having a romp?

Hanky-panky, aggressive Frenching, snogging, snorgling, extended bouts of tonsil-hockey, and performance of the horizontal mambo all cause moisture to be released into your ride’s cabin at an accelerated rate, which causes heaps of fog. Avoid having a romp in your ride, and if that’s not feasible, make sure the A/C is on, the recirculation is off, and that warm, dry air is directed to the windscreen.

Keep the climate control system healthy

A healthy climate control system can go a long way to reducing foggy windows. Be sure you’re a/C system is healthy, that your blower fan is working properly and not making any funny noises, and that your climate control intake isn’t blocked with leaves or debris. Further, replacing a clogged cabin air filter can make a tremendous improvement to climate control system performance, which will de-fog your ride even faster.