Get Rid Of

How to Stop Condensation Inside Car Windows

Updated · 5 min read

A car windshield fogged up on the inside, blurring street lights at night
Photo: AhmadElq, CC BY-SA 4.0, via Wikimedia Commons

Short answer

Fog forms inside a car when warm, damp air touches cold glass. To clear it, use the defrost setting, keep the A/C on, and switch to fresh air instead of recirculate. To stop it coming back, take out the moisture: dry wet floor mats, don't leave wet things in the car, clean the inside of the glass, replace the cabin air filter, and find any leak that's soaking the carpet.

Quick steps

  1. To clear fog now: defrost on, A/C on, fresh air (not recirculate), and fan on high.
  2. Take wet floor mats, umbrellas, and gym bags out of the car to dry overnight.
  3. Clean the inside of the windshield and windows with glass cleaner.
  4. Replace the cabin air filter if it's old or the airflow is weak.
  5. Check the carpet for damp. A wet carpet means a leak that needs fixing.

Need supplies? Jump to what to buy

Why car windows fog up

Air holds water as an invisible gas. When warm, damp air touches glass that’s colder than its dew point, the water condenses into tiny droplets. The National Weather Service explains that the dew point is the temperature air must cool to before this happens. Inside a car, your breath and anything wet raise the humidity, and cold glass does the rest.

1. Clear it fast

Consumer Reports’ fastest fix:

  • Turn on defrost. In most cars it turns on the A/C and sends air to the windshield.
  • Keep the A/C on, even in winter. The A/C dries the air. You can still set the temperature to warm.
  • Use fresh air, not recirculate. Recirculate keeps the damp air inside. Outside air in winter is usually drier.
  • Crack the windows for a minute if it’s still slow.

Don’t wipe the glass with your hand. It leaves oil that makes the next fog worse.

2. Take the moisture out

Fog that keeps coming back means the car is holding water.

  • Floor mats. Snow and rain from shoes soak into them. Take them inside to dry overnight, or swap carpet mats for rubber ones in winter and empty them.
  • Wet things. Umbrellas, towels, gym clothes, and coffee cups add moisture all night.
  • A dehumidifier bag. A reusable silica dehumidifier left on a seat or the floor soaks up moisture while the car is parked. Dry it out when the beads change color.

3. Clean the inside of the glass

A film of dust, smoke, and residue from vinyl gives water something to cling to, so dirty glass fogs faster and clears slower. Clean the inside of the windshield and windows with glass cleaner and a microfiber cloth, including the bottom edge of the windshield.

4. Replace the cabin air filter

A clogged cabin air filter cuts airflow to the windshield, so it clears more slowly. If it hasn’t been changed in a year or the fan feels weak on high, replace it. It’s usually behind the glove box.

5. Find any leak

Press a dry paper towel into the carpet in each footwell and in the trunk. If it comes up wet, water is getting in through a door seal, window seal, sunroof drain, or the windshield seal. The fog will keep coming back until the leak is fixed and the padding underneath is dry. Our car smell guide covers drying out wet carpet.

If the inside of the windshield has a greasy film and the car smells sweet, have a mechanic check the heater core for a coolant leak.

The same thing at home

Window condensation in a house has the same cause: damp indoor air and cold glass. See condensation on windows.

What to buy

We may earn a commission if you buy through these links, at no extra cost to you. How this works

Reusable silica car dehumidifier

wisedry Rechargeable Silica Gel Dehumidifier, 2 x 500 g

Soaking up moisture in a parked car overnight so the windows fog less in the morning. Also works in closets and gun safes.

Good to know: The beads change color when full. Dry them in the microwave as the label says, and keep the bag off the dashboard so it can't slide while you drive.

Check price on Amazon

Common questions

Why am I getting condensation inside my car?

There's more moisture inside the car than outside, and the glass is cold. The moisture usually comes from wet mats, snow on boots, wet clothes, your breath, or a leak in a door seal, window seal, or sunroof drain.

How do I stop my car windows fogging up overnight?

Take out everything wet, dry the floor mats indoors, and leave a reusable silica dehumidifier bag in the car. If the windows are still wet every morning, look for a leak soaking the carpet.

Should I use hot or cold air to defog the windshield?

The A/C matters more than the temperature. Consumer Reports explains that air conditioning dries the air, so you can set the heat to warm and still get dry air. Use the defrost setting, which turns the A/C on in most cars.

Why does my windshield fog up on the outside?

In humid weather, a cold A/C chills the glass below the outside air's dew point, so moisture condenses on the outside. Use the wipers and turn the temperature up a little so the glass isn't as cold.

Why is there a greasy film and a sweet smell on my windshield?

That can be a leaking heater core spraying coolant into the cabin. Have a mechanic check it soon. Coolant is toxic, and the leak gets worse.

Sources