How to Defog a Car Windscreen & Stop Condensation in Winter

Jack Dreyer | Wednesday 13th December 2023 12:00pm

A foggy car windscreen dripping with condensation in winter.

Winter brings snug evenings on sofas, chilly walks wrapped in wool, and (unfortunately) a lot of time spent warming up our cars! Other than having to wait longer for the engine to warm up and having to constantly be on alert for black ice, one of the biggest challenges drivers face is keeping car windows clear from condensation.

Let’s learn about stopping condensation.

Where does condensation come from?

It helps to understand what causes your windscreen & windows to fog up if you’re going to take steps to avoid it.

Fundamentally, condensation forms on surfaces where two different temperatures meet. The outside air in winter, for example, is generally quite cold – and while the internal temperature of your car isn’t usually high enough for condensation to form when you get in, the warmth of your body and breath usually increases the temperature just enough to cause condensation.

Think about it this way: your breath is roughly the same temperature as your body – so any moisture in your breath and the air in front of it can be warm enough to stay as a vapour. But when you breathe into cold outside air, you can often see your breath fog out in front of you.

The more humidity there is in your car’s air, the more (and more quickly) the windscreen and windows will fog up when you get in.

Is condensation in a car a problem?

Condensation forming isn’t a problem, but having a consistently humid car interior certainly might be. Other than the fact that it’ll take longer to defog your car, condensed water has to go somewhere – and that somewhere tends to be downwards towards areas with sensitive electrical or mechanical components. Over time, this can cause those components to rust, short circuit, and break.

So it’s certainly worth keeping condensation to a minimum!

If you’re finding that your car takes excessively long to defog, or fogs up again quickly – a window or door seal may have perished and be letting in more air & moisture.

Here’s how to defog a windscreen & stop as much condensation forming.

Turn on your car heater

Your car’s heater works by drawing heat from the engine and passing that heat into the interior of your car – so it often takes a minute or two to start getting hot because you have to wait for the engine itself to get hot.

To speed up the window demisting, set your heater to max power and turn it to the setting that directs all the output to the windscreen. This also has the added benefit of not blasting you directly with chilly air!

All being well, the mist should go within a few minutes and you can get on with your drive.

A person warming up by their car heater in a big coat.

Turn on your rear-window heating element

Many modern cars now come with a rear window that has a heating element embedded in it. This is essentially an electrical wire that has a current passed through it in order to heat up.

This feature was primarily designed to defrost rear windows but also works well to defog them!

Open your windows

Condensation forms when there’s a temperature difference, so your choice is to either warm the car up enough that the windscreen itself becomes warm, or cool the car down enough that condensation doesn’t form. To do this (which is sometimes a faster solution) – simply open your car’s windows.

However, this comes with the main drawback that you then have to drive while being freezing – and this only works well if the outside air isn’t especially humid. It won’t work especially well, for example, if you’re stuck in fog or heavy rain.

Keep your windows clean

This is often surprising, but condensation takes a lot longer to clear from grime that’s accumulated on the inside of windows than it otherwise would because it has a lot more to hold on to!

Making sure your windows are clean not only helps you see better but helps avoid condensation clinging on.

Use your air con

Heating the car up vaporises the condensation so you can see through your windscreen, but this moisture doesn’t actually go anywhere. Every time you drive, you’re essentially adding to the moisture content of the car because (funnily enough) you have to breathe while driving.

This means that you get into a vicious cycle of warming up the air when you get in only to have to warm it up more the next time you want to drive.

A clever way to really reduce the moisture content of your car is actually to run the air con system. It seems counter-intuitive to actively blow cold air into the car but the cold air isn’t what helps here: most air con systems have a dehumidifier in the cold circuit. So even just leaving the air con running on cool for a few minutes while the engine warms up will dehumidify a lot before you get the heater on!

Another thing to try alongside the above tips would be using dehumidifying pods. You can buy small non-powered dehumidifier packs online or from many supermarkets; just pop one or two in your car to help keep any damp at bay and replace them when they get full.

Is your car winter ready?

Driving in winter comes with the hazards of reduced visibility, component strain in the temperatures, and having to drive on wet, snowy, or icy roads. Make sure that your car’s winter ready with expert servicing & maintenance at your local Kwik Fit centre.

Any facts, figures and prices shown in our blog articles are correct at time of publication.

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