Why do windows steam up on the outside? Condensation on car and home windows explained - and how to prevent it

A cosy sign of encroaching winter or a nuisance? Here’s how to prevent steamy windows

Once the temperatures outside start to drop, steamed-up windows quickly become a permanent fixture of many UK homes and cars.

While a window dripping in condensation may provide faux privacy for a short while or signify time to throw another log on the fire, they can also be unattractive, and allowing moisture to build up in your home can contribute to the growth of harmful black mould.

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What causes condensation?

(Photo: Shutterstock)
(Photo: Shutterstock)

When moisture contained within warm air meets with a surface that is cold enough to turn it back into a liquid (condensation), windows can become foggy.

Window panes are especially susceptible to wetness in the winter, when the temperature difference between the outside world and the inside is at its greatest.

While you might be toasting away nicely indoors, external windows can still be subject to frigid temperatures, especially if they’re only single-glazed.

This big difference in temperature is the reason that windows become especially foggy in the winter.

(Photo: Shutterstock)

How do I get rid of condensation?

Getting rid of condensation that has accumulated on your window needn’t require any specialist or expensive equipment.

You can even make a simple, home-made solution to aid you.

Mix two cups of water with two cups of white vinegar and a few drops of washing up liquid.

Place this mixture into a spray bottle if you can find one, this will help you apply it to the glass equally.

Squirt the solution straight onto the window, and use a soft cleaning cloth to wipe it down again, leaving the glass to air-dry once you’re finished.

This simple solution will come in handy even if you’re not trying to shift condensation, and also works as an all-purpose window cleaner.

Bare in mind that if there appears to be moisture between the two panes of a double-glazed window, you will have to call a window professional to repair or replace it.

How do I prevent condensation?

Annoying condensation can be avoided before it becomes a problem of course, and there are a few things you can do to prevent condensation from building up in the first place.

Humidifiers or moisture eliminators can draw excess moisture from the air, but these can also leave rooms feeling dry, as well as being expensive to run and often noisy.

One tip is to avoid leaving wet clothes to dry inside your home, as the water from them will add to the moisture in the air.

A tumble dryer makes sense here if there's no way for you to dry your washing outside, but do make sure it has an external vent leading outside of your home, otherwise you will be faced with the same problem.

In the kitchen, keep the lids on your pots and pans as you're cooking to lock steam in, and if you have extractor fans make sure to use them.

Likewise, fans in the bathroom should be left running for 15 minutes after you’ve finished showering, and opening a window can let warm, moist air out.

How do I stop condensation on my car windows?

Of course, condensation on a house window is one thing, but a fogged up windscreen that impedes your driving ability can be dangerous.

Most wind screens have anti-fog measures built in, so clearing them is just a matter of pressing a button.

But older cars may require some ingenuity on your part.

Start the heater off cold, then slowly increase the temperature as the air dries out, rather than overloading the cabin with hot, moist air.

Make sure your heater's blast is directed at the windscreen and the windows - the warmer air will dry the glass a little through evaporation and begin to heat it up, which will stop water vapour condensing again.

To avoid a foggy screen in the first place, you can actually clean it with shaving foam, a little trick employed by ice hockey players to stop their face masks steaming up.

You might need to repeat this method regularly as the foam’s effect wears off, but a windscreen cleaned with shaving foam will be less likely to mist up.