How to Defog Car Windows Fast

Have you ever driven down the road on a rainy day with fogged up car windows and wondered, "How do I defog these quickly?" Then, you look at other cars next to you at a stop light, and their windows are crystal clear. What are you doing wrong? How can you fix it fast?

  • The most common mistake people make is hitting the recirculation button on their climate control (heater control panel). When this button is pushed, the blower motor will open a vent door inside the vehicle, causing the blower motor to draw air in from the cabin of the vehicle, hence the term (recirculation).
  • When the climate control is in recirculation mode, the blower motor sounds like it's moving more air because the fan gets louder inside of the car, the fan sounds louder, but it's only because the recirculation door is open. If you are recalculating the air inside the vehicle and there is moisture inside your car, it will start to accumulate on your windows.

How to Clear Up Fogged Up Car Windows

If you have fogged car windows, here's the best way to defog them quickly:

  1. Stop recalculating the air in the vehicle and turn on your air conditioner. The air conditioner will remove the moisture inside the vehicle by circulating the air through the cold fins in the evaporator, which will turn the humidity in the air, back into a liquid, and remove it from the inside of your car.


  • If your air conditioning does not work, you will have to turn your blower on full defog and open your windows just a little to allow the moisture to escape.
  • Do not use recirculation at any time unless your air conditioner is working properly. Using it without AC will only cause problems.

Other Causes

Here are some other common causes of foggy car windows:

  • If your floors are wet in the vehicle, and there is no good explanation for it—like if you left your window open in a rain storm—you may have a water leak in your vehicle. It's not uncommon to have water leaks and even new vehicles could leak water into the cabin through a split seam, or a seam that was not sealed properly from the factory. It doesn't happen often, but it does happen.
  • If you have had your windshield replaced recently, it may not be sealed properly. This is very common, especially if the person who replaced it did the job in 15 minutes. A good technician will take anywhere from one to two hours to replace a windshield properly.
  • A leak in your heater core could also be the culprit. If you start your engine and your windows fog up immediately, and you smell something sweet like candy, chances are your heater core is leaking. Engine coolant or antifreeze smells and even tastes sweet, that's why animals drink it and get very sick or even die. Never leave it out where kids or animals can get to it.
  • If you notice a colorful fluid (usually green or orange) leaking on the floor from under the dash, that could be a sign of your heater core leaking. Heater core leakage is not that common these days, but some do fail. The cost of replacing one is very expensive on most vehicles—generally you have to remove the dash to get to it.

If You Own a Newer Vehicle

  • Most newer cars are manufactured with climate control, so the user doesn't have to decide what buttons to push to defog the windows.
  • On new cars, when using the windshield defogger, the air conditioning automatically comes on even if you are using the heat. It acts as a dehumidifier, clearing your windows quickly and efficiently, simplifying your driving experience even more so you never have to think about what button to push for the quickest results.

Tip: To increase your visibility in the rain, I highly recommend using Rain-X on all your vehicle windows. Driving at night with it on your windshield improves visibility. Best of all, you don't even have to use your wipers unless it's raining very hard. That's just my experience. It also repels dirt and debris from sticking to the glass, which means less cleaning for you.

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Comments 36 comments

wilderness profile image

wilderness 5 years ago from Boise, Idaho

Foggy windows is a problem for us; we have a small car and often carry 4 people. You are correct, though, that the climate control automatically runs the AC when on Defog and it sure helps.

eddiecarrara profile image

eddiecarrara 5 years ago from New Hampshire Author

Yes wilderness, using the AC is the fastest way to clear fogged windows, I notice a lot of kids driving with friends in the car have fogged windows, I want to roll down the window and say something, but I'm sure they would just laugh. Thanks for the comment

Tinsky profile image

Tinsky 5 years ago from Brisbane, Australia

I once drove 804.31 km (or about 499 miles) in a strange car in very rainy and windy weather (we had a small cyclone following us down the coast) before we discovered how to turn on the demisters. Right about this time the rain cleared up. Climate control is an extra luxury item in cars in Australia I believe, I don't think its standard.

eddiecarrara profile image

eddiecarrara 5 years ago from New Hampshire Author

That makes for a long ride Tinsky when you can't see out your windows. You are still able to clear them without air conditioning, but it take longer, most people make the mistake of turning on recirculation, which in turn, makes it impossible to clear the windows. Thanks for the comment :0)

frogyfish profile image

frogyfish 4 years ago from Central United States of America

Cool video talk...useful tip for me to remember! Thanks!

eddiecarrara profile image

eddiecarrara 4 years ago from New Hampshire Author

Thanks frogyfish, I'm a little nervous behind the camera but I feel it's easier to show and tell sometimes, and it leaves a lasting impression. I feel I can explain it better in a video and I think people will retain it longer if they see it, rather than read it. Thanks for the comment :)

Melly 4 years ago

Thanks for posting this! My husband and I just moved from Florida to Indiana, and we were not prepared for the foggy car windows. While it seems like total common sense (invite less-humid air into the car, and push the a/c button to dehumidify), we didn't think to do either of these things, and sat in our car like morons trying to defrost the windows quite a few times. In an old car that doesn't have a defog button, your suggestions were super helpful!

eddiecarrara profile image

eddiecarrara 4 years ago from New Hampshire Author

That is awesome Melly, I know it's seems like a no brainer but there are a lot of people that have never had it explained to them, just last night I helped some guy sitting at a atop light with this problem, he looked at me kind of strange but thanked me as he drove off, lol. I'll never know if he took my advice. Thanks for the comment.

chris 4 years ago

I have one question though: when you use the A/C, do I need to set me temperature to full hot or full cold, or does it matter? Because my confusion is that when I switch to full front defog, my A/C automatically turns itself on.

eddiecarrara profile image

eddiecarrara 4 years ago from New Hampshire Author

Hi Chris, you are right, on the newer cars the AC automatically come on in defrost mode for maximum clearing power. It doesn't matter what temperature it's set at as long as the AC is running. The heat and air conditioning is achieved by opening and closing doors inside the cars duct work. There are 2 doors in the ductwork, one for fresh air or reticulated air from the passenger's cabin, and the other door is for the heater core.

Air is constantly being pushed through the evaporator, but if the AC compressor is not running, the evaporator will not be cold, and it will not remove moisture from the air.

If you have just the AC on, the heater core door is closed allowing the air to pass through the evaporator and bypass the heater core for maximum cooling.

If you have just the heat on, the AC compressor is not running, the evaporator is ambient temperature and the heater core door is open for maximum heat.

When you have it on defrost mode, the AC compressor is running, the evaporator is cold and it is removing moisture from the air that is passing through it, then the dry air passes through the open door to the heater core, warming it, then the warm dry air is pushed out in the vehicles passenger compartment.

The only reason the AC has an option to turn off is for fuel economy, otherwise it would run constantly. When you run the AC system, the compressor puts a drag on the motor, causing the engine to work harder and use more fuel.

Chris 4 years ago

Wow, you really know your stuff! Thank you very much! This has cleared up my problem about fogged up windows. And I encourage you to inform others like you said even if you're stopped at an intersection. They may look at you strangely, but later on they'll realize "hey remember what that guy said about fogged windows?". And it will in general make driving safer for others. Thanks again!

eddiecarrara profile image

eddiecarrara 4 years ago from New Hampshire Author

Thanks Chris, I am humbled by your comment,. Don't forget to vote up the article, it helps my overall score and I would really appreciate it. If you have any other automotive questions, please feel free to ask, or just take a look at my other articles. Take care.

EddieGul 4 years ago

Hi Eddie, I was searching for answers online and came across to your post. I watched your VDO and found it very informative, thanks for uploading. I have a 2000 Land Rover Freelander 2.0 TDi4 and my problem is even worse. I live near Siberia, where the temp is like -37 °C (opposite of hell). As soon as I start my car, the car turn foggy and it looks like there is a sheet of ice on all the windows and windscreen. Despite the car heater is turned on it keeps blowing cold air, freezing my nuts to death. I can't turn on the AC in such a low temperature and freeze myself as a mummy, so I am not sure know what to do. Is there something wrong with the thermostat, coolant system, heater-core, etc. I have no idea! If you have any suggestion, please let me know. Thanks!

Shawzy 4 years ago

Hi, I found this info very useful as I always switched the AC off when using the windscreen defogger and my windows were always steamed up, thanks.

You know your stuff so I was wondering if you could help me out. I have a Lexus 2.2 diesel when I use the climate control in winter to heat the cabin up the engine revs higher when the car is idle, sitting in traffic for example until the car reaches running temperature, is this normal?

Do cars in general with or without climate control use more fuel in winter due to using the heaters? The reason I ask ask is I have noticed a difference of about 4 mpg between summer and winter. I also have a Clio 1.5 diesel without climate control and have noticed a difference of 10 mpg between summer and winter.

Any help would be much appreciated, thanks.

eddiecarrara profile image

eddiecarrara 4 years ago from New Hampshire Author

Hello Eddie, You live in Siberia??? That's cool, no pun intended, lol. It sounds like your heater core has a leak or you have a mass of amount of moisture inside the cabin from bringing in snow on your boots. But the key factor is the windows fog up as soon as you turn on the heater, so it sounds more like a heater core or even a coolant hose leaking in the car.

I'm not familiar with Land Rover and how the heat is plumbed into the car. You can have the ac on with the heat, but it's unlikely the compressor will cycle in those temperatures unless you can heat the passengers cabin to 40deg or warmer. I would check your coolant level when the engine is cold (parked out side for 5 seconds with the engine off in Siberia, lol)Check the radiator and the overflow tank, if the coolant is low you probably have a leak.

Top off the radiator and the overflow tank with coolant, (most automotive coolant comes premixed 50% coolant 50% water , just check the label) Look under the hood to see where the coolant hoses enter the vehicle, then go under the dash in that location and see if you have any wet spots on the vehicle floor, if you don't see any leaks, run the engine till it reaches normal operating temperature or a 1/2 hour, this will build up pressure in the cooing system, the leak should be easy to find at this point.

Coolant has an oily feeling to it and it has a sweet smell like candy, do you smell this inside your car? If you do it's sure sign of a heater core leak. Let me know what happens Eddie, I'm curious to know the problem, thanks, take care.

eddiecarrara profile image

eddiecarrara 4 years ago from New Hampshire Author

Hello Shawzy, Thank you for your comment, I'm happy to help so many people with this problem. I live in the US and I'm helping people like Eddie in Siberia, how cool is that :) Let's address your Lexus question.

It is normal for the engine to idle faster when the engine is cold, this is caused by the fast idle valve. The fast Idle valve is usually controlled by coolant running through it, once the coolant reaches a predetermined temperature, the idle will drop to base idle.

As far as the fuel consumption goes, all cars use more fuel in the colder months because the engine runs at a higher rpm when warming up and for a longer period of time. In the warm months, my engine never even goes on fast idle when the engine is cold. I believe most fast idle valves start working when the temperature is below 60 deg, but this will vary between car manufactures.

Using the heater does not use more fuel, using the AC will use more fuel because the AC compressor puts a load on the engine when it cycles on. The heater only uses the blower to push air through the heater core. The heater core is a small radiator stuffed inside your dash, coolant is pumped, from the water pump, through the tubes inside the heater core, and then air flows over the tubes to extract the heat, so there is no extra pump needed for heat, unlike the ac compressor. I hope this answers your question, take care

Shawzy 4 years ago

Hi Eddie, thanks for answering my questions it's much appreciated, just to let you know you really are helping people worldwide, I live in Scotland not quite as cold as Siberia though not far off it lol :)

The reason I wasn't sure about the engine revving higher when using the climate control is my other car a Renualt Clio 1.5 diesel and other cars I've had without climate control don't fast idle when using the heater before the engine reaches optimum temperature. Just to confirm is it only cars with with climate control systems that fast idle until the engine is warm?

I was concerned about about the drop in mpg in both cars as a gallon of diesel is an eyewatering $9.30 over here so fuel economy is important to me.

Eddie the world would be a much better place if there were a lot more people like you that are willing to help people without trying to rip them off.

Thanks, shawzy

eddiecarrara profile image

eddiecarrara 4 years ago from New Hampshire Author

Hi Shawzy, All the way from Scotland... very nice to meet you :) The cars with climate control automatically turn on the air conditioning when using defog/defrost, so if the ac compressor kicks on, the idle will rev higher as well. On some cars you can adjust the fast idle so it's not so noticeable when the ac kicks on, older Honda's had this feature, maybe you could ask a trusted mechanic in town if your car has this fast idle adjustment.

So the answer to you question is, the engine should only rev higher if the ac compressor kicks on, it really doesn't mater if you have climate control or not. If you have a manual button to turn off the ac, I would use it to save fuel and only use ac when necessary. I can understand your pain with the fuel prices being so high, diesel in the US right now is about $3.50 gal and I think that's a lot,lol. Thank you for your kind words Shawzy, let me know if you have any more questions, I really like helping out :) Take care

Stephen 4 years ago

I just bought a 2001 Daewoo Lanos and it's currently winter where I live, so I can't turn on the AC but my windows constantly become foggy and the defrost doesn't help?

eddiecarrara profile image

eddiecarrara 4 years ago from New Hampshire Author

Hi Stephen, You can use your ac with heat, this will remove the moisture form inside your car. If that doesn't work, turn the heat on high, fresh air not recirculated, and open the windows about 1 inch so the moisture will escape. It will take a bit longer this way but it will work. Let me know if this helps:)

Shawzy 4 years ago

Hey Eddie, my Lexus fast idles when the engine isn't up to operating temperature all the time when I use my climate control even without the AC on, I questioned this with my local Lexus dealer and they said this was normal. My previous car was the same (new Honda civic 2.2 deisel). My brother in law also has a deisel car and he said his does the same, I was wondering if it is only deisel cars that do this? I was in Florida last year on holiday and I hired a Chevy camaro (petrol engine obviously lol) and it never fast idled at all even with the air con on...confused??

P.s. I wish I could afford to run a camaro over here, what a machine!!!! :)

eddiecarrara profile image

eddiecarrara 4 years ago from New Hampshire Author

Hello Shawzy my friend, glad to see you come back with more questions. I actually don't know much about diesels, heck, I never even heard of a diesel civic in the 25 years working at a Honda dealership, lol. It is possible that diesel motors need a higher RPM when there is an electrical load, like the blower motor, head lights, and rear defogger. If the dealer says it's normal, I would have to say their right.

You're right about the Camaro, you probably didn't notice the bump in the idle with the ac on, manufacturers try to make the transition from base idle to fast idle as smooth as possible. I am very impressed by how far the Camaro has come, if you like that car you really need to check out this Super Snake Mustang, My favorite car has always been the Shelby Cobra but this car is my next runner up :)750 HP with cup holders lol

Hey, I learned something from you today about diesels, so if you ever need answers to more automotive questions , you know where to find me. I really appreciate you coming back to ask more questions, the more I learn, the better I can help other people. Take care and don't forget to check out that video, it's very cool!

Jodytoons 4 years ago

We just got a 2012 CR-V! (about a week ago) Great car, but it is really foggy! The 03 Element we traded in, hardly ever had this problem, and this new car has a lot of condensation on the inside. Usually taking up to 15 minutes to clear. We will try the non-recirculating air tip, but this car probably already has the AC activated when Defrost is on. We'll have to test and see if we can turn the AC on as well as defrost....I read up above, where you said, if you crack the windows that might help as's incredibly annoying especially in such a new vehicle. (However it is winter in the Midwest, and when one's feet are's hard to control. Thanks for the advice! Much appreciated.

eddiecarrara profile image

eddiecarrara 4 years ago from New Hampshire Author

Hi Jody, That is really surprising! One more thing you can try is washing the inside windows with glass cleaner, sometimes the people prepping the car for delivery don't wash the windows on the inside, there is a film on the windows from the factory that causes your windows to fog abnormally if it's not cleaned properly. Give that a try and let me know what happens. Thanks for you comment :)

Shawzy 4 years ago

Hey Eddie, as the old saying goes you learn something new everyday lol :) must just be one of the downsides of owning a deisel!

The 2.2 civic diesels are very common over here, but diesels in general are popular and sought after over here compared to the US, due to the price of fuel and diesels being more economical.

Believe it or not diesels are more expensive to buy than the petrol equivelant models!!

I watched the YouTube link, man the sound of that super snake mustang gave me goosebumps! Awesome! I dream of owning a big meaty V8 one day, it will probably never happen but I can always dream lol. I did a supercar trackday 2 years ago got to put a lamborghini gallardo 5.0 V10 and a Ferrari 360 Modena V8 through there paces, both awesome machines too.

I've been to the US a few times and I absolutely love it, love the culture and the way life, I would love to live there some day. I've been to Florida , Nevada, Arizona, and California.

It's been good chatting to you, you seem like a nice, genuine guy :)

eddiecarrara profile image

eddiecarrara 4 years ago from New Hampshire Author

Hey Shawzy, thank you for those kind words. It seems you have visited more places in the US than I have,lol. I'm jealous you got to drive those cars, I have always wanted to got to one of those open track days, but I have never had the opportunity, but I have driven a Porsche 911 turbo, 85mph in first gear...YIKES!!! But I think the Super Snake is it's competition.

Thanks for stopping by again, it's good to hear from you, and if you ever need any advice, come on back, I think I'll be here a while, lol. Take care :)

Lois 4 years ago

2001 Jimmy Heater only 125km core was replaced 1 month ago now it blowing up again why? It was a big job the first time now again. There is antifreeze on the front passenger mat. Help the heater core replaced was from do l have to now get a GMC heater core? Hence my window are foggy too. near Kamloops, BC

eddiecarrara profile image

eddiecarrara 4 years ago from New Hampshire Author

Hello Lois, Did you replace it yourself or did you have a mechanic do it? If it's a reputable garage you should have a 90 day parts and labor warranty.

Unless you had a defective heater core installed, I really don't think that's your problem this time. Either the heater core was damaged on installation or maybe one of the hose clamps is not tight on the heater core and is squirting into the car (I know that's a long shot, but you never know)

I would bring it back to the shop that installed it, you payed to have it replace once, I don't think you should pay twice. Unfortunately, if you replace it yourself, the only thing that is under warranty is the part, and that job must have been intense!

Let me know what happens, I'm curious to know what's leaking.

Jason Seattle 4 years ago


Well I have a serious fog issue. I own a 1996 Saturn Wagon. In 1997 I had a roof rack in stalled. Ive lived in Texas and Southern California up intil recently I just moved to Seattle and the fog has just started. The inside of my front windsheild gets so extemly foggy ,sometimes when im driving that I literally cant even see the road. Its so bad Im thinking of buying a new car but I dont have money to spend. I am certain that the person who installed my roof rack did it incorrectly... bending plastic and breaking the seal on my roof. I know for a fact because at some point in 1997 water was leaking down my back window and the Saturn dealershp used some sort of silicon caulking around my back window. OK.. SO... Ive tried EVERYTHING to try to defog my front inside wind sheild. Today I made alitle headway by filling up with 50/50 antifreeze. This has helped the heater get hot. But, I'm still trying to figure out the best way to defog the front windshelid. If I'm correct by reading your posts... I should turn the heater on full blast and shoot the hot air up through the windsheld, turn off the recirculation button, and turn on the AC buttin. Does that sound right ? Im just about to loose my mind. Ive also been told to get an AC service. What should I tell them to do specifically to fix my AC if my AC is indeed broken. I ve ruled out a heater core problem because i dont smell any antifreeze in my car. And Ive recently got the ''thermostate'' replaced so I know its not that. Thanks for any insite. I appreciate your thoughtfulness in your responses. Sincerely, Jason in Seattle

eddiecarrara profile image

eddiecarrara 4 years ago from New Hampshire Author

Hello Jason,

Seattle? Isn't it cold and damp there? And you came from hot and dry, you must be going crazy, you never had to deal with this stuff.

If you AC is inop, it won't do you any good to run it because the evaporator will not collect the moisture and remove it. You could have your AC fixed but it might cost you a few bucks.

The best thing you can do Jason is to crack your windows about an inch and turn the heat on high defog, and do not recirculate the air, put it on fresh, it takes a lot longer this way but it does work. You should always have 50/50 coolant in the engine to protect it from corrosion.

Give that a try and see what happens, if you can fix your AC that would help immensely and if you could dry out the inside of your car that would help too, maybe take off the roof rack and fill the holes with bondo or fiberglass filler. Let me know if this works for you, talk to you soon.

bdegiulio profile image

bdegiulio 3 years ago from Massachusetts

Eddie, this is really, really useful information. I have a 96 Saturn also and it's always had a problem defogging the window. I always do exactly what you say to not do, hit the recir button as it gives the impression of the fan blowing harder? Now I know what not to do and what to do. I never considered using the A/C but it makes perfect sense now that you have explained it. I'll give it a try. Thanks so much, this is great information. Voting up, sharing, etc....

eddiecarrara profile image

eddiecarrara 3 years ago from New Hampshire Author

Hey Bill,

Yeah, the re-circulation button is a bit confusing, but if your're using the AC, it's really doesn't matter if it's on or not because the AC is a dehumidifier. In my opinion, the only time you should every use the re-circulation button is in hot and humid temperatures. Thanks for the comment, vote, and sharing Bill.

jperlingos 2 years ago

My situation is a little unique. I went to get my car detailed the week before last and they put the washed car mats in my car wet apparently. The car looked great until the next day when the windows all got this waxy film all over them and I can barely see through the window, I got my car washed again and asked them to clean the window good, but the film is still there, it was so bad on my driver side window that you can write with your finger. I was told to try soap and vinegar or ammonia, or may Window Wax, which is a total hassle. Please let me know what I can do to get the wax film from whatever they did to my car off my windows. Thanks!

eddiecarrara profile image

eddiecarrara 2 years ago from New Hampshire Author

Hi jperlingos , the first thing I would do is dry the carpets by letting the car idle in you driveway for about 2 hours with the heat on full blast and the windows cracked about a 1/2 inch. Next, take a spray botttle and put a drop of Dawn dish soap and fill the rest with water (nothing else). Buy some Sparkle paper towels (no lint paper towels) and clean the windows. Let me know if this helps.

peter 3 days ago

turtle wax soap rubbed onto the windows works with a cloth

eddiecarrara profile image

eddiecarrara 14 hours ago from New Hampshire Author

Thanks Pete, I appreciate the input ;)

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