Car windscreens mist up with condensation because the water vapour inside your car is warmer than the outside temperature and the temperature of the car's glass. Pretty annoying when you need to get on the road to attend a meeting you're already running late for or to get the kids to school. Plus, it's also important that you clear condensation from your car windows before driving off. Not only are misted windows a safety hazard for you and other road users, but driving with impeded visibility is illegal and could land you a fine!
Fortunately, modern cars are designed to deal with misted glass during start up or if it happens mid-journey. Read on for some tried and tested advice on quickly clearing that glass and keeping it clear. It's all about using your car heater or air-conditioning correctly…
TOP TIP: before doing anything else, make sure that your car's heater, air-con or climate control isn't set to 'Recirculate'. If this is on, your efforts to demist the car will be doomed from the start because the moist interior air will simply be moved around inside the cabin! Bear this in mind when you are en route. The recirculate function has an important role if you need to avoid traffic fumes entering the vehicle, but leaving it switched on for longer than necessary will mist up your car interior!
Using your car's air-con or heater correctly is the key to fast, efficient demisting. We'd recommend that you start by reading or re-reading the relevant sections in your car's printed or online owner's manual. The manufacturer's engineers have invested lots of time and money to design an effective system. You owe it to them and yourself to make sure you know how your car's heater, air-conditioning or climate control works.
Let's start with a conventional heater. Counter-intuitively, it's important to start your heater on the cold setting when you need to demist the windows.
Once air is moving around the car interior and windscreen, you can gradually use the heater controls to increase the temperature of air reaching the windscreen. Doing this helps because the 'cold start' minimises overloading the cabin with hot, moist air before the warm air heats the cabin and the surface of the windscreen glass.
It sounds obvious, but you need to make sure that you've selected the best heater and vent settings to direct as much air over the windscreen. The interior ventilation systems of most modern cars are designed to direct air over the front passenger windows too. Even 'cold' air from the heater should be warmer than the windscreen glass.
Here's another tip: consider cracking open the window a few millimetres too, or leave the driver's door slightly ajar. Doing this can help because it allows cold, dry air from outside to help reduce the amount of water vapour trapped in the cabin.
Most modern cars have air-conditioning, if not the added luxury of climate control. Air-conditioning (aka air-con, A/C or AC) uses a powerful fan to draw air into the car's cabin from outside. The system removes unwanted warmth and moisture from the air and pumps it out of the vehicle.
Think of air-conditioning as a fridge for your car. The good news is that, as well as cooling the car on hot summer days, the physics behind its operation also helps to remove water vapour and stop condensation forming on the inside of the windows.
If you've got air-con, try the approach we recommended for a vehicle with heating only. Having started with the system on cold, gradually increase the temperature. Then switch the air-conditioning on. The latter will keep the car's interior atmosphere as dry as possible and minimise the likelihood of any residual moisture condensing on the windscreen again.
If you think that your air-conditioning isn't working as well as it should, the system could need recharging. To find out more about an air-conditioning service for your vehicle, contact your local garage.
Climate control is a computerised system that uses the car's air-conditioning to maintain temperature. Depending on your car, you may be able to set different levels for one or more areas of the car interior – including a demisting option for keeping the windscreen and other glass free of condensation.
Climate control allows you to manage the interior temperature and humidity of your vehicle very precisely. You select a required temperature, then leave the automated system to adjust the temperature accordingly. Compare this to air-con where you manually adjust the temperature, fan speed and where the airflow is directed (for example, the footwell or, for demisting, onto the windscreen).
You only need to spend a few minutes searching online to find a wide variety of products that claim to reduce misting on car windscreens. These include anti-fog glass cleaner fluids, anti-mist wipes and reusable de-humidifying packs that absorb moisture. As an alternative to proprietary anti-mist cleaning fluid, some people (including the RAC) recommend using shaving foam!
We've never tried applying shaving foam to the inside of a windscreen, then polishing it off to give anti-condensation protection. However many lots of online articles, including the RAC's, do recommend this hack. If you've got some lying around (we've no idea whether shaving gels work as well), you could always give it a whirl. It might prove to be 'the best anti-mist treatment your windscreen can get'!
A few simple tips should help you minimise unwanted water vapour in your car interior. Here are some things you can do:
If you regularly experience excessive condensation, it might be worth checking that wet clothing or other items aren't regularly left in the car. It's also worth checking to see whether your cabin air filter is blocked. Finally, extreme cases of persistent condensation might indicate that water is leaking into the vehicle. It happens, due to faulty heater matrices, damaged rubber door seals or leaking sunroof surrounds. They're all worth checking.
Hopefully, by following this guide you can achieve efficient windscreen demisting and get on your way as fast as possible. And, of course, you'll be driving with optimum visibility and keeping on the right side of the law!