# Does leaving the car window down an inch actually cool it off?
**URL:** https://boards.straightdope.com/t/does-leaving-the-car-window-down-an-inch-actually-cool-it-off/497928
**Category:** Factual Questions
**Created:** [May 28, 2009, 2:37pm UTC](https://boards.straightdope.com/t/does-leaving-the-car-window-down-an-inch-actually-cool-it-off/497928 "2009-05-28T14:37:49Z")
**Posts on this page:** 20
**Page:** 1
### Author:  [@MsWhatsit](https://boards.straightdope.com/u/MsWhatsit)
#### Post date: [May 28, 2009, 2:37pm UTC](https://boards.straightdope.com/t/does-leaving-the-car-window-down-an-inch-actually-cool-it-off/497928/1 "2009-05-28T14:37:49Z")
I see people doing this a lot in the summertime around here. On a hot day, they’ll crack their car windows by 1-2", I guess on the assumption that it will allow air to circulate so that their car will only be as hot as the surface of the Sahara Desert when they get back, instead of being as hot as the surface of the sun.
Does this actually work?
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### Author:  [@scr4](https://boards.straightdope.com/u/scr4)
#### Post date: [May 28, 2009, 2:51pm UTC](https://boards.straightdope.com/t/does-leaving-the-car-window-down-an-inch-actually-cool-it-off/497928/2 "2009-05-28T14:51:16Z")
If you mean “is the logic valid,” yes. Usually a surface exposed to direct sunlight will get hotter than the surrounding air. If that surface is the roof of a sealed car, the interior gets hotter than the outside air as well. So opening the window will lower the interior temperature.
If you mean “does a 1-inch gap really make a noticeable difference” - that depends on wind speed, outside temperature, color of the car, etc.
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### Author:  [@Little\_Nemo](https://boards.straightdope.com/u/Little_Nemo)
#### Post date: [May 28, 2009, 3:02pm UTC](https://boards.straightdope.com/t/does-leaving-the-car-window-down-an-inch-actually-cool-it-off/497928/3 "2009-05-28T15:02:02Z")
My unproven assumption is that the air is circulating inside the car. As the sun heats the car, the hot air inside is rising to the top of the car. So with a gap in the car windows, some of the circulating air inside is going to move out of the car. And being as the gap is near the top of the car, this air is the warmest in the car and the air from outside that replaces it will be cooler.
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### Author:  [@scr4](https://boards.straightdope.com/u/scr4)
#### Post date: [May 28, 2009, 3:08pm UTC](https://boards.straightdope.com/t/does-leaving-the-car-window-down-an-inch-actually-cool-it-off/497928/4 "2009-05-28T15:08:27Z")
I suspect outside wind is more important than any natural convection current inside the car, even on a seemingly calm day. Especially if you crack open windows on both sides of the car, so wind can push air into the car from one side and out the other.
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### Author:  [@x-ray\_vision](https://boards.straightdope.com/u/x-ray_vision)
#### Post date: [May 28, 2009, 3:20pm UTC](https://boards.straightdope.com/t/does-leaving-the-car-window-down-an-inch-actually-cool-it-off/497928/5 "2009-05-28T15:20:14Z")
According to researchers at Stanford University School of Medicine:
> [@](#):
>
> Their study, published in the July 2005 Pediatrics, documented that on sunny days, even if the temperature is a relatively cool 72 degrees, the inside temperature of the car will reach 117 degrees within 60 minutes of turning the car off (and will top 108 degrees within 30 minutes!). Leaving the windows open 1.5 inches made no difference in the final temperature or the rate of rise.
> **[Cars: Hotter Than You Think](https://www.drgreene.com/cars-hotter)**
>
> Kids (and pets) left alone in cars have died from heat stroke on days as cool as 70 degrees Fahrenheit. How can this be? We all know that on hot August
This part is a little ambiguous:
> [@](#):
>
> On hot days, the rate of rise is the same, but dangerous temperatures can be reached within 5 minutes of closing the car doors, even if the windows are cracked.
The rate of rise is the same, but it’s unclear whether or not the same final temperature will be reached on hot days.
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### Author:  [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)
#### Post date: [May 28, 2009, 4:05pm UTC](https://boards.straightdope.com/t/does-leaving-the-car-window-down-an-inch-actually-cool-it-off/497928/6 "2009-05-28T16:05:33Z")
My own personal experience strongly disagrees with your Stanfrod study. When I am at work, leaving the windows cracked just 1 inch makes a huge difference in the temperature of my car at the end of the day.
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### Author:  [@x-ray\_vision](https://boards.straightdope.com/u/x-ray_vision)
#### Post date: [May 28, 2009, 4:10pm UTC](https://boards.straightdope.com/t/does-leaving-the-car-window-down-an-inch-actually-cool-it-off/497928/7 "2009-05-28T16:10:57Z")
> [@engineer\_comp\_geek](#):
>
> My own personal experience strongly disagrees with your Stanfrod study. When I am at work, leaving the windows cracked just 1 inch makes a huge difference in the temperature of my car at the end of the day.
What kind of day? A “relatively cool 72 degrees” day or a “hot” day?
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### Author:  [@Quartz](https://boards.straightdope.com/u/Quartz)
#### Post date: [May 28, 2009, 4:54pm UTC](https://boards.straightdope.com/t/does-leaving-the-car-window-down-an-inch-actually-cool-it-off/497928/8 "2009-05-28T16:54:54Z")
I think the problem here is that the air coming in to the cabin has to go via the car’s ventilation system, so (a) there’s a small volume of air coming in and (b) the air gets heated along the way before it enters the cabin.
I wonder what the effect of leaving the windows wide open would be - other than your car getting stolen, of course.
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### Author:  [@Sapo](https://boards.straightdope.com/u/Sapo)
#### Post date: [May 28, 2009, 4:58pm UTC](https://boards.straightdope.com/t/does-leaving-the-car-window-down-an-inch-actually-cool-it-off/497928/9 "2009-05-28T16:58:58Z")
> [@Quartz](#):
>
> I wonder what the effect of leaving the windows wide open would be - other than your car getting stolen, of course.
Then I guess it depends on whether the thief turns on the A/C or not. 😉
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### Author:  [@Zsofia](https://boards.straightdope.com/u/Zsofia)
#### Post date: [May 28, 2009, 5:49pm UTC](https://boards.straightdope.com/t/does-leaving-the-car-window-down-an-inch-actually-cool-it-off/497928/10 "2009-05-28T17:49:00Z")
I don’t crack my windows when it’s in the 70’s. I do when it’s over 100. It definitely makes a difference.
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### Author:  [@zut](https://boards.straightdope.com/u/zut)
#### Post date: [May 28, 2009, 5:57pm UTC](https://boards.straightdope.com/t/does-leaving-the-car-window-down-an-inch-actually-cool-it-off/497928/11 "2009-05-28T17:57:55Z")
> [@x-ray\_vision](#):
>
> According to researchers at Stanford University School of Medicine:
>
> [http://www.drgreene.com/21\_1957.html](http://www.drgreene.com/21_1957.html)
>
> This part is a little ambiguous:
>
> The rate of rise is the same, but it’s unclear whether or not the same final temperature will be reached on hot days.
This is kind of an interesting drift of information. Your cite quotes the following paper:
“[Heat Stress From Enclosed Vehicles: Moderate Ambient Temperatures Cause Significant Temperature Rise in Enclosed Vehicles,](http://pediatrics.aappublications.org/cgi/content/full/116/1/e109)” Catherine McLaren, MD, Jan Null, CCM and James Quinn, MD, \*PEDIATRICS \*Vol. 116 No. 1 July 2005, pp. e109-e112. (This might be restricted content, so I don’t know if the paper is generally available.)
The paper says this:
> [@](#):
>
> On 2 of these days, recordings were made first with the windows closed. Then the doors were opened to return the vehicle to ambient temperature, and a second hour of measurements was made with the windows cracked 1.5 inches. It was ensured that no significant change in ambient temperature occurred during these 2 hours.
>
> […]
>
> **Comparison of Closed Versus Cracked Open Windows**
> Figure 4 illustrates a nonsignificant trend to faster heating in the first 20 minutes with the windows closed 6.25°F per 5 minutes (95% confidence interval [CI]: 1.0–11.5) versus 5.5°F per 5 minutes (95% CI: 1.2–9.8) with the windows cracked open. However, overall, \*\*the rate of temperature rise for windows that were cracked open was 3.4°F per 5 minutes (95% CI: 2.4–4.4°F) compared with the rate for closed windows of 3.1°F per 5 minutes (95% CI: 1.4–4.8°F), \*\*with the final temperature for both circumstances being identical. (my bold)
Note that this confirms that there is no difference in the final temperature, but the rate of rise _is_ different.
Now, this paper, in turn, cites a previous paper:
> [@](#):
>
> King et al found that in an ambient temperature of 36.8°C (98.2°F), 75% of the maximum temperature rise occurred within 5 minutes of closing the doors and maximized within 15 minutes to 51 to 67°C (124–153°F). **Opening the windows 20 cm (8 inches) had minimal effect on the temperature rise and maximum temperature attained**. (my bold)
So let’s look at _that_ paper:
“[Heat Stress in Motor Vehicles: A Problem in Infancy,](http://pediatrics.aappublications.org/cgi/reprint/68/4/579?ijkey=c1e23c9f94945a3ac999ad87637fc99c48ed177c)” K. King, K. Negus and J. C. Vance, _Pediatrics_1981;68;579-582. (a pdf; again I don’t know if it’s generally available.)
> [@](#):
>
> The effects of ventilation were assessed using three large white sedans with brown interior trim. One car had closed windows; the second and third had all four windows opened 50 mm and 200 mm (halfway), respectively.
>
> […]
>
> **The vehicle with windows open 200 mm was significantly cooler than the vehicle with windows open only 50 mm. Likewise, the latter was cooler than the closed vehicle.** The stabilized interior ternperatures for the three vehicles were as follows: closed vehicle, 66.4 C; windows open 50 mm, 50.5 C; windows open 200 mm, 40.9 C (ambient temperatare 36.8 C).
>
> […]
>
> \*\*Substantial reductions in interior temperature were only achieved by opening the vehicle windows by at least 200 mm \*\*(halfway) for the test sedans. This action gives internal temperatures approaching ambient, approximately 40 C compared with 36.8 C. This degree of window opening increases the risk of theft,2 and restraining the child within the car may be more difficult. A “compromise” opening of 50 mm, although resulting in a temperature drop of more than 15 C over the closed vehicle temperatures, still produced a temperature 13 C above ambient. Thus, “cracking” the windows contributes little to the creation of an acceptable interior environment. (my bold)
Note that the _actual data_ from the King paper _directly contradicts_ what the later McLaren paper says–not just contradictory data between the two experiments, but McLaren _ **actually mischaracterized the data obtained by King** _.
In addition, the McLaren paper shows temperature rise for “cracked” windows that has an unexpected, unusual shape over time. I suspect their experimental procedure (“[R]ecordings were made first with the windows closed. Then the doors were opened to return the vehicle to ambient temperature, and a second hour of measurements was made with the windows cracked 1.5 inches.”) is flawed, although admittedly that’s hard to say with certainty. However, the mischaracterization of the earlier results does not give me confidence in the McLaren paper, and thus the Dr Greene site–although admirably cautionary–does not strike me as conclusive evidence.
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### Author:  [@Squink](https://boards.straightdope.com/u/Squink)
#### Post date: [May 28, 2009, 6:06pm UTC](https://boards.straightdope.com/t/does-leaving-the-car-window-down-an-inch-actually-cool-it-off/497928/12 "2009-05-28T18:06:25Z")
> [@](#):
>
> On 2 of these days, recordings were made first with the windows closed. Then the doors were opened to return the vehicle to ambient temperature, and a second hour of measurements was made with the windows cracked 1.5 inches. It was ensured that no significant change in ambient temperature occurred during these 2 hours.
I’m curious as to whether they also controlled for the 30° movement of the sun over the course of these two hours, and if so, how.
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### Author:  [@Cheesesteak](https://boards.straightdope.com/u/Cheesesteak)
#### Post date: [May 28, 2009, 6:09pm UTC](https://boards.straightdope.com/t/does-leaving-the-car-window-down-an-inch-actually-cool-it-off/497928/13 "2009-05-28T18:09:56Z")
> [@zut](#):
>
> I suspect their experimental procedure (“[R]ecordings were made first with the windows closed. Then the doors were opened to return the vehicle to ambient temperature, and a second hour of measurements was made with the windows cracked 1.5 inches.”) is flawed, although admittedly that’s hard to say with certainty.
It all depends on how long the doors were left open when returning the vehicle to ambient. If they opened the doors, flapped them a few times and waited a couple of minutes, there’s no way this procedure is sound. The seats, floor, roof and dash would all still be significantly hotter than ambient, and will foul up the results. Use 2 identical cars, and alternate cracked vs. closed instead of always doing cracked second.
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### Author:  [@zut](https://boards.straightdope.com/u/zut)
#### Post date: [May 28, 2009, 6:22pm UTC](https://boards.straightdope.com/t/does-leaving-the-car-window-down-an-inch-actually-cool-it-off/497928/14 "2009-05-28T18:22:04Z")
> [@Cheesesteak](#):
>
> It all depends on how long the doors were left open when returning the vehicle to ambient. If they opened the doors, flapped them a few times and waited a couple of minutes, there’s no way this procedure is sound. The seats, floor, roof and dash would all still be significantly hotter than ambient, and will foul up the results. Use 2 identical cars, and alternate cracked vs. closed instead of always doing cracked second.
Exactly my point. The irregular shape of the data curve and the non-intuitive result (as well as the mischaracterization of earlier data) makes me think _something_ is awry. If nothing else, consistently running the “cracked” trial _after_ the “closed” trial, rather than alternating or randomizing the trials, is poor experimental design and the results should be called into question just because of this.
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### Author:  [@cjepson](https://boards.straightdope.com/u/cjepson)
#### Post date: [May 28, 2009, 6:26pm UTC](https://boards.straightdope.com/t/does-leaving-the-car-window-down-an-inch-actually-cool-it-off/497928/15 "2009-05-28T18:26:22Z")
> [@Quartz](#):
>
> I wonder what the effect of leaving the windows wide open would be - other than your car getting stolen, of course.
That definitely makes a huge difference. If I’m at home and know I’m going to be using the car in, say, half an hour, sometimes in summer I’ll go out and open all the windows. Over the course of that half hour the temperature in the car will drop from oven-like to pretty much whatever the outside temperature is.
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### Author:  [@x-ray\_vision](https://boards.straightdope.com/u/x-ray_vision)
#### Post date: [May 28, 2009, 6:38pm UTC](https://boards.straightdope.com/t/does-leaving-the-car-window-down-an-inch-actually-cool-it-off/497928/16 "2009-05-28T18:38:49Z")
Nice work, **zut**. 🙂
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### Author:  [@Turek](https://boards.straightdope.com/u/Turek)
#### Post date: [May 28, 2009, 7:31pm UTC](https://boards.straightdope.com/t/does-leaving-the-car-window-down-an-inch-actually-cool-it-off/497928/17 "2009-05-28T19:31:30Z")
And \*after \*the nice work?
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### Author:  [@x-ray\_vision](https://boards.straightdope.com/u/x-ray_vision)
#### Post date: [May 28, 2009, 7:38pm UTC](https://boards.straightdope.com/t/does-leaving-the-car-window-down-an-inch-actually-cool-it-off/497928/18 "2009-05-28T19:38:44Z")
Pardon?
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### Author:  [@silenus](https://boards.straightdope.com/u/silenus)
#### Post date: [May 28, 2009, 7:52pm UTC](https://boards.straightdope.com/t/does-leaving-the-car-window-down-an-inch-actually-cool-it-off/497928/19 "2009-05-28T19:52:21Z")
Bad, wicked **zut**. 😃
**X** , it’s a Monty Python [reference](http://pythonline.com/node/3976061).
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### Author:  [@Sapo](https://boards.straightdope.com/u/Sapo)
#### Post date: [May 29, 2009, 12:43pm UTC](https://boards.straightdope.com/t/does-leaving-the-car-window-down-an-inch-actually-cool-it-off/497928/20 "2009-05-29T12:43:23Z")
> [@zut](#):
>
> Exactly my point. The irregular shape of the data curve and the non-intuitive result (as well as the mischaracterization of earlier data) makes me think _something_ is awry. If nothing else, consistently running the “cracked” trial _after_ the “closed” trial, rather than alternating or randomizing the trials, is poor experimental design and the results should be called into question just because of this.
Good catch.
Do we have any reason to suspect an intention to eschew the results for a particular purpose? Is any of these studies funded by a company selling cooling fans, a group against animal cruelty, child abuse, etc? Or is it just sloppy science?
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