Windows vs A/C


#1

No, it’s not about whether my computer runs on alternating current.



Were Tom and Ray just repeating the old saw about closing the windows and running the A/C to save gas, or do they (or anyone else) have actual data (perish the thought) supporting this.



I ask because Consumer Reports say that their tests – real data! – consistently show that this is not true:



http://www…/index.htm



Edward


#2

And the “Mythbusters” tested this, twice I think, and their results showed that at speeds greater than 50 mph it was more efficient to run the AC.


#3

Agreed, Mythbusters checked it out too, not that the guys are any smarter than Consumer Reports…


#4

Thanks. Seems to be 2005 episode 38. Unfortunately I can’t find it either on their site or on Youtube. I’d be interested in reviewing their techniques. (And those of CR too for that matter.) My guess is that it’s going to depend a lot on the design of the car body, and that manufacturers probably don’t put a lot of work into the aerodynamics of the open-window situation.

Edward


#5

Don’t discount improvements in AC compresser efficiency. In the 70’s AC compressors took much more hp to turn and did not have any power saving features like variable displacement.

My favorite way to answer this very common question is to state that windows up AC off is best for fuel mpg.


#6

I can’t say for every car, but in my 2001 VW GTI, running the A/C makes a noticeable difference in the gas mileage, around 5 MPG or more. I’ve driven this car for six years, I calculate MPG with every tank full and I can say without a doubt that as soon as I have to start using the A/C in the summer instead of running around everywhere with the windows (and often the roof) open, my mileage takes a nose dive.


#7

Well put. On a recent vaca. with my 01 Taurus, checking mileage with a/c on and then with it off, it made only a mpg or 2 difference. But I never ran with windows down either.


#8

It will vary from car to car and the drive and the way you drive. In most cases at highway speeds, you will get better mileage with the windows closed, A/C on.


#9

Best for mileage is windows up, AC off.In reality driver technique (or lack of) will influence mileage more.

We don’t really discuss the fact that AC compressors from 2010 use much less horsepower than a AC compressor from the 70’s. I mention this as some people develope a way of thinking about the automobile that comes from a certain time period and then every conclusion about the automobile comes from this same time period, just human nature I guess.


#10

I will shift gears even if I have no sychronization and have to double clutch, I will build up my arm muscles and do without power steering, I will do without power brakes and step on the pedal with both feet. I’ll go back to crank windows or even side curtains, but I will not give up air conditioning. If I lose a couple of miles per gallon, it is worth it. I would bet that on the highway, using the air conditioning beats rolling down the windows.


#11

I grew up without A/C in either car or house. In Florida. I know how to use fans. I know how to survive. I ain’t going back either.

Edward


#12

Most of my driving is done on the highway, so if it?s hot enough that I need to choose between one or the other, I choose AC, not only because I think at those speeds the mileage is better, but I don?t want the noise and air blowing around either.

1 or 2 mpg doesn?t sound like much, but I drive an ?02 Taurus, and that would probably be like the difference between 25 and 23 mpg (I drive too fast) for me. 2 mpg doesn?t sound like much when you say ?a couple of miles per gallon,? but that?s an 8 percent decrease on those numbers. That?s pretty substantial. Or it would be like paying 8.7 percent more per gallon ? or almost 23 cents on $2.60 a gallon gas!

Couple miles per gallon sounds pretty significant when you think about it in those terms, I think. I?ll pay a few bucks to keep from getting sweaty while I?m driving, but I might not do it as often now!


#13

Same here, except in Illinois, and with almost no heat in the winter. It sucks getting up to go to school, coming downstairs to find the front door blew open overnight and it’s 30 degrees in the house. The only thing worse is trying to sleep in an 85 degree house with 85% humidity. The car I rode in as a kid was a 1971 Chrysler New Yorker station wagon that not only had no a/c or tinted windows, but had a black leather interior. Talk about a scorcher! I’m not going back to those days either. I will sacrifice 2mpg to ride in comfort, and even sacrifice whatever it adds to my power bill each month to keep my house cool. I don’t know the figure on that one because I always keep my house comfortable, and I haven’t been living here very long, maybe four months. I don’t really care, either. I like to be comfortable.


#14

Since the others have covered all the bases, I would only like to add that (A) today’s cars are much quieter than cars of decades ago, but only with the windows up, so having the windows open would mean a big increase in noise; and (B) for most of us, quiet and comfort are worth the 1.5 or 2 MPGs we might be giving up. Where I live, the heat index is expected to reach 111 degrees(F) today.


#15

On top of that, lots of modern cars are extra noisy with the windows down because of the reverberations that occur, like blowing over a pop bottle, that result from the aerodynamics of modern designs. So those really aren’t candidates for windows down driving.


#16

I grew up walking to school in the snow. Uphill both ways. In Buffalo. Barefoot.

My father inherited a 1980 Chevy van from his mother, and that thing had an aftermarket air conditioner installed. That thing never worked right.

Before Floridians had air conditioning, they had houses designed to stay cool without it. Some of those houses are still standing. They have screen doors on every room, and every room opens to a breezeway. They have the kitchen separated from the rest of the house by one or more breezeways. You could stick one fan in the breezeway and cool the whole house. Today’s Florida homes aren’t likely to even have an attic fan, which I think is the next best thing.


#17

Before Floridians had air conditioning, they had houses designed to stay cool without it.

Uh … what they had were houses designed to make the best of the situation, which indeed differs from modern house designs which assume a/c. But having grown up in Florida, lemme tell you that “designed to make the best of it” is most definitely not the same thing as “designed to stay cool”! There is no such thing as cool in Florida between the end of April and the start of October. You go for months with the temperature never dropping below 70F at night, and the reason it doesn’t go any lower is because it’s reached the dew point. “Cool” is not possible under those conditions.

It’s no accident that the really explosive population growth in Florida, the thousand people a day moving into the state, started when a/c became common in houses, around the 1950s and 1960s. (I don’t have a table of the actual immigration figures.)

Edward


#18

My late mother taught in a one room school house in central Illinois during the depression. The school did not have electricity, nor did it have running water. She was expecte to fire up the coal stove in the morning. She walked about 4 miles each way from the small town where she grew up to the schoolhouse. The salary was $100 a month for 9 months. I would hear about her adventures teaching in this school, particularly when I would complain about the school bus I rode being cold in the winter.


#19

When I was doing graduate work at Southern Illinois University, one old building where I had classes had windows on two sides of the classroom and high ceilings. There were wall mounted fans in the room but no air conditioning. This room in many ways was more comfortable than the classroom where another class I took was held that was air conditioned, but had no windows and a lower ceiling. The most uncomfortable building for me during the summer of 1964 was the library. The air conditioning system had failed and it had to be over 100 degrees in the stacks. I would go in and work for an hour, go outside where it was only 85 to cool off and then go in for another hour of torture.

None of us had any money back then. We didn’t have air conditioned cars nor were our rooms air conditioned. I guess I have become soft in my old age, but I want that air conditioning.


#20

Whether it’s cheaper to run with the AC no or the windows open will be highly dependant upon the car, the speed, and the headwinds. There is no “always correct” answer.

Personally, I think when I open my roof and the windows it’s cheaper. Or maybe it’s just more fun, so the cost isn’t as important.