Windshield frosting on INSIDE?

I live in Ann Arbor, MI. I’ve noticed on a few recent cold mornings that there is frost on the INSIDE of my windshield as well as on the outside. I’ve had this car a couple of years, and this has never happened before with it… or for that matter with any other car I’ve ever had.

Why is this happening, and what can I do to prevent it from happening again? And if it does, how best do I get the frost off the inside of the windshield? The scraper doesn’t work on the slight curvature.



The frost is forming on the inside because there’s moisture in the car. Perhaps it came from snow on your shoes when you get in. Perhaps there’s a leak somewhere. For whatever reason, there’s enough moisture in the car to condense on the inside of the windows and freeze there.

Do you keep the climate control setting on “recirculate?” If so this might be contributing to the problem. Set the control to “outside air” and operate the AC to dehumidify the air. Yes, it’s OK to run the AC in winter. The heater will still work, even with the AC on.

I suggest checking around on the floor to see if there is wet carpet anywhere. Lift the floor mats and check under them. Leaving a window open slightly on a warm, dry day might help get rid of the moisture, assuming there isn’t a lot of it.

If there’s water somewhere, you have to get it dried out in order to stop the condensation.

Getting rid of frost on the inside is easy; turn on the defroster and set the temperature and fan control to high. The frost will melt within a few minutes.

High humidity trapped inside the car does this. Happened for me too.
You are bringing in the moisture on your feet in this weather, no matter how much you kick off the snow. It stays in your floor mats and carpet which never really have a full chance to dry.

Untill the weather gets better ;

  • Don’t park with the heater system in any of the recirculating modes.
  • Get some good ol’ school chalk sticks and place them in various areas in the cabin like door pockets and under the seat. They are a good absorbant.
  • Given enough time before parking, Open a window a tad and turn the heater on high to expel some humidity.
  • If the weather’s ok, take out your mats to bask in the sunlight to dry.

I did these thing to my 06 Escape hybrid when it frosted up the winters of 06 & 07.
It has not ever happened since. The school chalk is still in the door pockets and under the seats.
“Hey, look what I found, Uncle.”
“Just leave it there, it’s a long story.”

This is not unusual. When you exhale, you exhale a certain amount of vapor. When you stop the car and leave, if the weather is very cold, this moisture plus any other moisture from snow you may have dragged into the car, condenses and freezes on the windshield. Dogs have it figured out–they drive with their heads out the window which keeps the moisture from their breath from condensing and freezing on the windshield.
If you go to your favorite bar for a cold draught, the mug will often be frosty on the outside. This is the moisture in the air condensing and freezing on the mug. The same principle applies to your windshield.

I Have No Idea What A Kia Rondo Is, But It Would Possibly Help To Know The Model - Year Of This Vehicle (car, truck, SUV ?). I Might Be Able To Find Some Information.

Do you make frequent short trips ? Are your driving patterns the same as they’ve always been ?

As others have suggested, get the floor good and dry. DIY car wash turbo-vacuums are a help with this. They are wet-or-dry vacs with lots of pull.

Once I get my cabin air up to temperature, I switch to full floor mode with plenty of heat and fan during the winter, just to keep my floor dry. A long trip of a couple hour’s duration, once in a while, helps, too. Frequent short trips during the winter tend to keep the floor and mats wet.


Thanks, That Sounds Good. I’m Going To Get A Beer In A Frosy Mug.


Don’t get around much, do you?

The Kia Rondo is a mini-minivan:

I would rather have the frost on the outside of my beer mug than the inside of my windshield.


Thanks, I Run Between Here And The Golf Course And High School Sports Events.
No Kias.


I don’t know but I been told
Ann Arbor Michigan is mighty cold!

The curvature of the inside of the windshield is the same as that on the outside, otherwise you’re driving behind a lens.

I blame the weather. It couldn’t hurt to leave your driver’s side window cracked a bit overnight.

Thank you, folks, for all the good replies and suggestions you’ve been sending. Some I’ve already tried, some are new and are worth trying. (I really like the school chalk one!)

I realized, just after I’d posted the question, that I’d forgotten to say what the car is. It’s a 2007 Kia Rondo, which is a crossover model, and the color is dark blue.

The carpet is soaking wet from all the snow. Yes, Ann Arbor gets very cold in winter. There’s been a fair amount of snow (though nothing like what so many of you everywhere else have been getting whacked with this year). But it’s like this every winter, and I haven’t had this problem before.

I usually have the heater all the way up and the fan on high when I’m driving. When the inside has been frosted, I’ve been doing as suggested, with the defroster setting on and the heat and fan both set at high. This still takes a good 5 or 10 minutes or longer for the frost to be gone, depending on how frosted up it is.

I took it to the dealer on Friday to ask about this. The service guy mentioned the climate control setting, which I’d always had off because I didn’t really know how it worked. He said have it open while you’re driving but close it before shutting off the engine. I did thate, and there was no frost this morning. None outside, either. (For that matter, what causes frost to form on the outside some cold nights and not others?)

Yes, the curvature of the window is the same inside and out, but outside it’s convex (so the middle of the scraper blade gets it), while inside it’s concave and only the very edges of the scraper get it.

I will definitely try out running the AC tomorrow and also cracking the window a bit. Thank you!

My driving is almost all short trips, and my driving patterns have not changed.

I blame the weather, too. (I HATE winter, grrrrr.)

That sounds like the best idea yet, to check out frost on the outside of a beer mug to see how my windshield frost compares.

Thank you, everyone!


One tip: When warmer weather comes, be sure that the carpet gets thoroughly dried out. You may have to pull up the carpet on the side and fold it back for a day to let it dry out. A soaked carpet will ultimately rust out the floor of the car.

Well the curvature is the same, but on the outside it’s convex and on the inside it’s concave. I had the same issue one -13 degree morning.

On a sunny day, park with the driver’s side toward the sun and leave the sunward window slightly open so the moisture will get out. The moisture is in the floor mats and carpet until it evaporates and forms ice inside the car.

Check the trunk in the cavity behind the wheel wells. If you have a window leak, ice will form there. A solid block of ice.

Thanks again for the further replies. I’ve been printing them out to take along when I drive so I can put them into practice.

Now to think: where can I drive to that will take me about two hours for the trip…