General Question

whitecarnations's avatar

Do you use hot or cold air when you are defrosting your windshields in your vehicle?

Asked by whitecarnations (1635points) March 24th, 2012

Always have this debate with the guys.

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18 Answers

Nullo's avatar

I use cold air. Using hot air causes the inside of the windshield to fog up, which is almost as bad. Sometimes I’ll just hang my head out the window and drive that way.

whitecarnations's avatar

@Nullo That’s funny.

I tend to use hot air, but with my fans full blasting. I don’t really notice a fog up as a matter of fact it becomes clear for me, but that’s with really hot air. Now, if I just hop into my car and turn on the hot air, obviously cold air will come out first and it’ll take probably 5 minutes for solid heat to come through. I think in the short term cold air is good. But long term the solid heat is good, plus usually its cold out in the rain. But I also think it’s just the fact that I’m blasting the fan really high that is getting rid of the fog up.

Nullo's avatar

@whitecarnations Ah, but I’m usually up against ice. And I’m always running late. And cranking the heat all the way on usually produces a weird smell.

cazzie's avatar

When I was in NZ we got the very occasional frost on the windscreen in the mornings. Instead of trying to melt it from the inside with the defroster, we took a hose or a bucket of water and poured it over the thin ice to melt it off. Some ninnies would use hot water, thinking they were smart, and the glass would crack. This only works if the outside temperature is above freezing of course. One of the benefits of living with palm trees in the yard.

I would say that some defrosters/heaters work better than others. The only thing I really know is don’t throw hot water on the windscreen.

whitenoise's avatar

We would use a combination of:
*) A/C on to take any humidity from the air and
*) heater on MAX to increase the temperature of the air to increase its ability to absorb the moisture / melt the frost from the inside of the screen.

silky1's avatar

I use hot air to defrost.

tedibear's avatar

I start the car, turn the defroster on heat, full blast. Then I start brushing the snow and scraping the other windows. I do the windshield last, and by the time I get there, I don’t have to do much ice scraping and the snow almost slides off.

marinelife's avatar

It depends on the condition outside the car. If it is humid and warm outside, I use cold air.

LuckyGuy's avatar

I live in a cold climate and must do this frequently. Sometimes we can go the entire month of January with the temperature never once getting above freezing.
I do what @tedibear does. Start the car Turn the defroster on (front and rear) then begin brushing the snow off the car hood, roof, windows trunk, and go back to the windshield. By that time the ice comes off easily.
On most cars, the defrost setting cycles the air conditioner compressor to prevent it from seizing up from disuse. Some manufacturers intentionally put the setting that turn on the compressor in front of the ones that don’t need it. Supposedly that away you momentarily cycle the compressor when you turn on the heat. However, lazy people often just leave the controls in one spot and are surprised 6–8 months later when they next need A/C and it does not work.

Here’s another tip we cold weather folks do. Warm air holds much more water than cold air. When I am returning from my drive and am about a mile from home I will open the windows and vent out the hot warm air from the car interior. That replaces the warm moisture laden air with cold dry air from the windows do not fog up .

elbanditoroso's avatar

Hot seems to work faster for me. Of course, when I start the car it’s cold, so there’s no effect until the engine begins to create some heat.

CWOTUS's avatar

I almost always use hot or warm air, sometimes with the A/C as well, if it’s a wet day (or if there’s moisture in the car from the outside atmosphere or snow melting off shoes and boots inside the car).

In warm, foggy weather when I also need “demisting” sometimes then I use the A/C and cool air.

digitalimpression's avatar

I use warm air. When there is frost on the window I’m usually cold as well.. and I would like to be warm. I’ve never had any issues.

Rock2's avatar

Use the air conditioner.

wilma's avatar

Hot, and I do it like @tedibear and @LuckyGuy .

simone54's avatar

Really? Nobody pointed out the that you’ll crack your windshield if you use hot water.

wilma's avatar

@cazzie did, ^^ up there.

Bent's avatar

I turn on the engine, turn the heater and blowers on and scrape. The air is cold to begin with and doesn’t really heat up fully in the time it takes to scrape off the ice, but it helps warm up the car a bit. My car doesn’t have AC but if it mists up I turn off the heat and blow cold air instead.

MissAnthrope's avatar

If I’m just starting the car up, I don’t have much choice, as has been pointed out. It’s cold until the engine warms up. In cold conditions, I’ve found that warm or hot air works most efficiently. I have had people adamantly insist I should use cold air, but I have experimented and it would seem that warm air defrosts things quicker. This makes sense to me because if you warm up the glass, no condensation should then form. It seems to me that using cold air on the glass is counter-intuitive (unless we are talking about hot, humid conditions).

“Condensation on a window occurs when the surface of the window is cooler than the “dew point” temperature of air in contact with the window. Condensation is a result of a combination of surface temperature and moisture in the air.” (via)

On my car, the defroster setting uses the A/C system, regardless of temperature. This is convenient sometimes, other times not (such as when driving long distances, I suppose my choice would be not to use up extra gas for the defroster). But oh well.. small quibble, really, since my car is a champ at defrosting and I’ve ridden in some where you couldn’t defrost/defog the windshield no matter how much you tried.

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