Picture the scene: it’s a freezing morning when you dash to your car. You jump into the driving seat and slam the door. You stick the key in the ignition and fire up the engine, ready to head off—but you’re not going anywhere quickly. Your windscreen is completely fogged up.
If this scenario sounds familiar, you’ve come to the right place. We’re going to tell you how to demist a windscreen and get on your way fast.
Why does your windscreen mist up?
Naturally, being able to see clearly out of your windscreen is an essential part of driving safely. But it’s also a legal requirement in the UK. Start driving with a foggy windscreen, and you could end up with a fine and points on your licence.
But what causes your windscreen to mist up in the first place?
The answer is in the way air holds water. The colder the air, the closer together the molecules, and the less space there is for water.
On a cold day, the air inside your car will be warmer than the air outside. And when you jump in that driving seat, your breath and body temperature make it both wetter and warmer still.
Then that warm air hits the cold windscreen (or rear window) and cools fast. The colder air can’t hold as much water, so it’s squeezed out and forms a mist on the glass.
All this means that the answer to how to demist a windscreen is based on one important factor: heat.
So how do you do it?
How best to demist a car windscreen: 5 tips
1. Use your climate control system
If you’re driving a classic motor without climate control, keep reading for tips that work for you. But for newer cars, your climate control system is your best friend for demisting windows.
Most systems will have buttons specifically for heating your windscreen and back window. There’ll be two of them, and each one usually has three squiggly arrows pointing upwards.
For the rear window heater, the arrows will be on a rectangle:
For the windscreen, they’ll be on a shape that curves at the top and bottom. It looks like the arc made by a windscreen wiper:
Press the buttons, and the system will automatically regulate the airflow in the car to demist your windows fast.
2. Use your heaters
You can get the same result without a climate control system by using your car’s heaters. (But don’t worry if they don’t work! We’ll get to your other options later.)
Turn your heaters towards your windscreen as much as possible and set them to full fan. When you first switch your engine on, the air will be cold, but that’s fine.
But wait—we’ve already said the key to demisting your windscreen is heat. So does hot or cold air clear a windscreen?
Well, when it comes to how to demist a windscreen fast, the answer is somewhere in between.
If you immediately pump lots of hot air into the car, it will warm the glass. But that air will be carrying moisture too. So the first thing that will happen is that the windscreen will get even mistier.
Starting with cooler air from your heaters then slowly increasing the temperature will warm up the windscreen more gradually. And the air won’t be carrying lots of extra moisture to add to the problem.
If you have a car with a super-efficient heating system, you may need to turn the temperature down. But if your heaters take several minutes to warm up anyway, you can put them on high from the start.
3. Switch on the air conditioning
If you have an air conditioning system in your car, it’s a great way to speed things along. Turning it on will draw the moisture from the air, so there’s less of it to fog up your windscreen.
It’s also an important way of helping your windscreen stay clear after it’s been demisted.
All the breath you exhale will carry moisture—and that goes double if you’re singing along with the radio! Using the air con will dry out the air and keep it from steaming up your windows.
4. Use warm water
All the above is fine for newer cars. But how do you demist a car windscreen in a vehicle that doesn’t have a climate control system or air con? Or where the heaters aren’t reliable, or don’t work at all? That’s a bit trickier.
But don’t worry. How to demist a windscreen in this case is a little different. But you can still get the job done fast.
If you’ve got heaters that only pump out cold air, don’t despair. Used with bottles of warm water they can still demist the front windscreen fast.
It’s a bit fiddly, but you can fill a couple of containers with warm water and place them on your dash. The water will warm the air from the heaters as it passes over the bottles, speeding up the demisting process.
And if your heaters don’t work at all, you can do the job with warm water only.
Put some in a bowl—you won’t need much—and soak a cloth in it. Then wipe the cloth over the outside of your windscreen. As well as getting rid of fog inside the glass, it will remove ice on the outside.
But it’s very important to use lukewarm water, not hot. Hot water on a cold windscreen is a recipe for cracking the glass.
Don’t forget your return journey, too. Fill a thermos flask with warm water and take a spare cloth with you. That way you can repeat the process when it’s time to head home.
5. Open your windows (a bit)
It’s important to make sure your windscreen is fully demisted before you start moving. But if it starts to fog up whilst you’re already on the road, opening your windows can help.
But can cold air demist a windscreen when it comes from open car windows?
It can. In this case, the cold air from outside lowers the temperature inside the car. That means the air is already holding less moisture when it hits the windscreen, so it doesn’t fog up.
The lower your window, the more cold air you’ll let in and the quicker the interior temperature will drop. So while that’s good for stopping fogging in its tracks, it may not be particularly comfortable for you or your passengers!
A good compromise is to open the front windows just an inch or two. If you have working heaters, this works better too. It allows the warm air to flow up the windscreen, rather than being sucked straight out of a wide open window.
Prevention is better than cure
So how do you get rid of a misty windscreen? Clearly there are lots of options. But what if you never had to worry about it in the first place?
Well… there’s a little-known tip that can stop your windscreen from fogging up. It comes from the world of ice hockey, where players use it to stop their masks steaming up. But it works every bit as well to demist a windscreen, rear window or any other bit of glass.
Spray some shaving foam on a cloth and wipe it over the inside of the window. Shaving foam includes substances called surfactants. They don’t stop the moisture in the air condensing. But they do stop it forming into droplets. Instead the water forms a flat sheet over the glass.
That flat sheet is much easier to see through than the domed surface of thousands of water droplets. So to the naked eye, there’s no mist.
Just remember to reapply the foam every so often to maintain the protection.
Note: for more advice, check out our list of tips for looking after your windscreen in winter.
What if the mist is on the outside?
Nine times out of ten, “How do you demist the front window?” means “How do you remove mist inside the window?”
But what if the problem is on the outside?
Yes, this really can happen. And it can happen very suddenly too.
Imagine driving along on a warm day. You’ve got the air con at full blast to keep you cool. You drive into a tunnel full of warm, moist air. Before you know it, your windscreen looks like someone’s thrown a sheet over it.
This can be both shocking and very dangerous. But try not to panic.
Fog on the outside of your windows is very easy to deal with. Just switch on your windscreen wipers, and it will be gone almost instantly.
How to demist a windscreen: the bottom line
There are lots of tools at your disposal if you’re trying to demist a front windscreen or a rear windscreen. A climate control system with window demisters makes life easy. But a combination of heaters and air con can be just as effective.
And if your vehicle doesn’t have those bells and whistles, using warm water and an open window can work well too.
Whatever option you use, the demisting won’t take long. And it’s time well-spent to help keep you, your passengers, and other road users safe.
How do you demist the front window?
As we’ve mentioned in this guide, you have 5 options: using your car’s climate control, using your heaters, switching on your aircon, using warm water, or opening your windows while you’re going along. If the mist is on the outside, try your windscreen wipers.
Does hot or cold air clear a windscreen?
Bit of both. You’ll want to warm your windscreen up gradually, because blasting hot air in the car will make the windows even less clear in the immediate term. That said, usually heaters will take a bit of time to warm up—and if that’s the case for yours, you can still turn them up to hot.
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