Why Do My Car Windows Steam Up?

If you own an older vehicle, you’ve likely experienced the annoying phenomenon of steamy windows, especially in colder weather. Steamy windows aren’t just frustrating, they can be dangerous, and impair your visibility. So, why do car windows steam up, and more importantly, how can you prevent and fix it?

Car windows fog up when warm, humid air inside the car comes into contact with the cold surface of the glass. The air’s moisture condenses on the glass, forming tiny water droplets that blur your vision. Here are some common causes:

1. Cold Weather and Temperature Differences: During winter, the outside temperature is much cooler than the inside of your car, especially if you had the heater on the last time you drove. This difference in temperature leads to condensation.
2. Moisture Inside the Vehicle: Moisture trapped inside your car is one of the biggest culprits of steamy windows. This moisture can come from wet clothing, shoes, or even just the natural humidity in the air. If you’re driving in the rain or snow, the moisture content inside your car is even higher.
3. Water Leaks: Water leaks inside your vehicle, whether from ripped door seals or perished window rubbers, a blocked sunroof drain, or even leaky gaskets or grommets introduce excess moisture into the cabin. Over time, this water collects and evaporates, causing your windows to steam up more easily.

There are a number of actions you can take to help keep your windshield and car windows clear of any mist. Some you can even do for free! Let us run through your options, starting with the quick and simple first. 

Yes! Opening a door window will help reduce steamy windows in the short term, by allowing outside air to circulate into the car and reduce the humidity inside the cabin. This balance between the interior and exterior temperatures can help eliminate the condensation on your windows. It’s a quick fix, especially if you’re driving, but it’s not always practical in cold weather when you’re trying to stay warm. You'll need a decent set of driving gloves, and maybe even a hat (or helmet).

Fit yourself some wind deflectors to help keep the air flowing without letting the rain in! 

Most vehicles made since the seventies come equipped with a built-in defogger button or demister heater setting for this exact problem. The system directs warm, dry air onto the windscreen and other windows, which helps to evaporate any moisture on the glass. 

Turning on your car’s air conditioning, even in winter might sound counterintuitive, but will also help to remove moisture from the air, in turn reducing condensation.

If your VW Bug heaters aren't working or you've got VW Golf heater problems, check out our guides here. 

Heated rear windows are more common than front, and first came about because it was considered cheaper to run an electrical element on the rear screen, than duct warm air from the front of the cabin, all the way to the back. If you own a particularly old classic car you may not have a heated window at the rear. In some instances you may be able to install one - we sell a heated window wiring kit to help, but if you only use the vehicle in fair weather you might prefer the aesthetic without. 

The heated front windscreen is a more recent development and was first delivered by Rolls Royce in 1969. For the same reasons a demister with warm air works, the heating element warms the glass and repels the moisture. 

Make a conscious effort to remove any external moisture sources from your vehicle. 

Remove or shake off any snow or rain from clothing and footwear before getting into the car. If you can, keep wet items like umbrellas and coats in the boot or luggage area, instead of the passenger compartment. 

If you have floor mats made of carpet, rather than rubber make sure they are not waterlogged, and remove them from the vehicle regularly to dry out. Rubber mats will collect water from shoes and clothing and might be easier to shake out when the weather allows... Just don't spill them on the floor! 

If you suspect your windows or doors are leaking, it’s important to fix the cause as soon as possible. This issue will typically show up as wet carpets, as water will run and collect at the lowest point of the vehicle. Left untouched, the water will soak into any carpet underlay and sound deadening and slowly rot the vehicle from the inside out. 

We've covered how to find and fix water leaks in another article. Have a read of that here. 

There are specialized anti-fog treatments available for car windows. These products create a thin, invisible layer on the glass that prevents moisture from sticking and condensing into fog. Applying an anti-fog solution, with the correct application cloth, to your windshield and side windows can make a noticeable difference, particularly in humid or cold conditions.

You can buy a car dehumidifier bag for less than lunch on the road, and it will help to absorb excess moisture inside your vehicle. These bags are reusable and are typically placed on the dashboard or under the seats. They are a great long-term solution for keeping the interior of your car dry and preventing fogged windows. When 'full' you simply dry them out with a microwave and re-use them again. 

Alternatively, cat litter or bags of rice left under the seat are a cheaper and crude alternative! 

Should the situation be really bad, buying or borrowing an electric de-humidifier is a great idea. You can run one of these for a day or two and it will suck all the moisture out of your vehicle, and collect it in a plastic pot. This is great news if you have a particularly complicated (modern) car or campervan, where removing the seats and carpet is too tricky or time-consuming to consider.

Lastly, in a bid to equalise the interior and exterior temperatures storing the vehicle inside a garage will absolutely help. Not only will it keep the rain out of the already mentioned window seals, but the ambient temperature will remain a little higher around the glass. If a garage isn't an option, a good quality car cover will act like a sleeping bag for your pride and joy, offering further insulation from the cold weather outside. 

We hope this guide has given you some good ideas for tackling the steamy windows and condensation your car this winter. 

Happy motoring.

Andy