How do I stop my car windows misting up?

Misting is condensation on cold glass, exactly as it is at home. Clearing it quickly is about drying the air rather than heating it, which is why air conditioning is the fastest method even in winter. Recurrent misting means water is getting into the car and staying there.

Safety

What you'll need

• Microfibre cloths
• Glass cleaner
• Dehumidifier bag for cars (optional)

Step by step

1. Turn on the air conditioning along with the heater.Air conditioning removes moisture from the air. It clears mist considerably faster than heat alone, even in winter.
2. Turn recirculation off.Recirculating keeps the same damp air in the car. Fresh air from outside is drier.
3. Direct the airflow at the windscreen and side windows.The demist setting usually does this automatically along with enabling the air conditioning.
4. Clean the inside of the glass properly.A film of grease and residue on the inside gives moisture something to condense onto. Clean glass mists noticeably less.
5. Find the moisture source: check the footwells for damp.Wet carpets from shoes, a leaking door seal, or a blocked pollen filter drain are the usual causes.
6. Check the pollen filter and its drain.A blocked scuttle drain lets water into the cabin filter housing and then into the footwell. Common and frequently missed.
7. Remove wet mats and dry them out of the car.A wet carpet mat can hold a surprising amount of water and evaporate it continuously.
8. Use a moisture-absorbing bag in the car if it stays damp.Silica or similar. Cheap, reusable by drying, and effective in a car that's parked outside.

Tips

• Leaving windows open a fraction when parked at home helps considerably, if it's secure to do so.
• Never wipe a misted screen with your hand — it leaves a greasy film that makes future misting worse.
• A car that smells musty as well as misting almost certainly has water in the carpets. Lift them and check the underlay.
• Anti-mist products work by leaving a surfactant film on the glass. They help, but clean glass and a dry car do more.

Common mistakes

• Using recirculation to demist — It keeps the same damp air circulating. Fresh outside air is drier and clears the screen faster.
• Heat without air conditioning — Heat alone is much slower than dehumidified air. Most cars enable air conditioning automatically on the demist setting.
• Wiping the screen with your hand — It leaves a greasy film that gives condensation a surface to form on.
• Ignoring damp carpets — They evaporate moisture continuously, so the misting never stops recurring.

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