To stop car windows misting up, switch the air-con on, turn recirculation off so fresh air comes in, point the airflow at the windscreen and raise the temperature gradually. Turn on the heated rear screen too. The air-con removes moisture from the air while the heater warms the glass, so together they clear mist far faster than either alone. If your car has a windscreen demist button, it usually sets all of this in one press. Wait until all the glass is clear before moving off, and keep fresh air flowing for the rest of the journey.
Why do car windows mist up?
Mist is condensation: water vapour in the cabin air turning into tiny droplets on the cold glass. The RAC puts it down to water vapour from your body heating the air inside the cabin. Every passenger breathes out moisture, wet coats and umbrellas add more, and on a cold, damp day the windows are the coldest surface in the car, so the water collects there first.
The Met Office describes this point as the dew point, the temperature at which condensation begins. Keep the glass warmer than that, or the air drier, and mist cannot form.
What is the fastest way to clear a misted windscreen?
- Air-con on. The RAC says to make sure the air-con is on to keep the atmosphere inside dry, using it together with the heater.
- Recirculation off. Recirculating traps the same damp air inside. The RAC's troubleshooting advice for a screen that will not clear is to keep the air-con on and recirculation off.
- Airflow to the screen. Direct the heater's blast at the windscreen and side windows, with the fan high.
- Heat up gradually. The RAC suggests starting with the heater cool and raising it as the engine warms, rather than blasting cold air straight away.
- Heated screens on. Use the heated rear window and, if fitted, the heated windscreen.
- Crack a window. Opening the windows slightly for the first minute lets the damp air out.
Should you use the air-con in winter?
Yes. Many drivers switch it off in winter, assuming it only cools the car. The RAC explains that the air coming out of the vents is dry, so the air-con works like a dehumidifier, and that using warm air from the system in winter is a great way to demist the windows. It recommends running the air-con regularly throughout the year, which also keeps the system in good working order.
Climate control systems often have an automatic setting that manages this for you. If yours has a demist button with a windscreen symbol, use it on damp mornings.
How do you keep windows clear on a long, wet journey?
- Leave recirculation off unless you are briefly passing through traffic fumes or a tunnel, then switch it back.
- Keep some airflow on the screen even once it clears, especially with several passengers.
- Put wet coats and umbrellas in the boot rather than on the back seat.
- Use rubber mats in wet weather, so water from shoes does not soak into the carpet and evaporate onto the glass.
- Avoid wiping with your hand or a sleeve, which smears skin oil onto the glass and makes it mist faster next time.
Day-to-day habits that keep moisture out of a parked car are covered in our guide on cutting condensation inside your car.
Is it legal to drive with misted windows?
No. Rule 229 of the Highway Code says you must be able to see before you set off, and that mirrors should be clear and windows demisted thoroughly. Annex 6 adds that windscreens and windows must be kept clean and free from obstructions to vision. The RAC describes driving with impaired visibility as dangerous and illegal. Wiping a small porthole is not enough; wait until every window you need is clear.
Why do some cars keep misting up no matter what?
If your windows mist badly every time, something is adding moisture or stopping the system working:
- A dirty interior screen. The RAC notes that regularly cleaning the glass helps stop misting. The greasy film inside gives droplets something to cling to; our guide on streak-free car window cleaning shows the method.
- A clogged cabin filter restricts airflow to the screen.
- Air-con low on refrigerant cannot dry the air properly.
- Damp carpets from a leak keep releasing moisture.
- A sweet smell with a greasy film on the glass can indicate a heater coolant leak, which needs a garage.
For glass that is properly clean inside and out, our vehicle glass cleaning starts from £20 and comes to your home or workplace.
Sources
- RAC: How to demist your windscreen in double-quick time
- RAC: Should you use your air-con in the winter?
- GOV.UK: The Highway Code, driving in adverse weather conditions (rules 226 to 237)
- Met Office: Dew
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