Tiny Choices Q&A: Car Windows: up or down?
By Karina | September 11, 2007
Welcome to Tiny Choices Q&A, where we open the floor for discussion on questions which ya’ll have submitted (read the first list of questions here).
Xuli asks in the Keeping Cool Sans A/C post:
I wanted to ask you about not using AC in your car because we try not to use it also. But then I read somewhere that it is best not to use AC if you are going under 55mph because it slows down your car’s gas efficiency, but if you are going over 55mph, having the windows open will actually cause enough of a drag on your car that you will use more gas than if you were using AC. Is that actually true, or a big lie fed to me by the oil industry to trick me? Or are there are other reasons to avoid AC as well? (I remember that there were problems with the chemicals used for coolants in the early 90s, but supposedly those were mostly resolved for cars made after 1995 or so? Or perhaps not?) I’m really curious about this!
This is something I’ve wondered about for some time. Last week, though, my electric/gas company sent out an email newsletter that I nearly deleted and it summarized tests conducted by the Society of Automotive Engineers (SAE), the Florida Solar Energy Center (FSEC), and Consumer Reports. (This is why I am stuck reading every newsletter that lands in my inbox!) Not surprisingly (as we’ve seen on many different environmental issues already) the three reports reached differing conclusions.
All three reports agree that the A/C off and the windows up is the most efficient option. However, the SAE test indicates that the windows down-A/C off option is LESS efficient than the A/C on option, while the FSEC and Consumer Reports option report the opposite. The SAE test DOES include some neat graphs, though, indicating what you suggested above, Xuli - that the efficiency is linked to the speed at which you drive, but the graphs do not suggest that driving speed will impact the how you should operate your vehicle.
I would conclude that if you can get by with the A/C off while your windows are up, you should do so, but otherwise, as long as you’re not using your A/C you’re being efficient.
Umbra tackled this question as well, and she offers some do-able tips such as window tinting and parking your car in the shade to avoid having to turn on the A/C. As for myself, when I’m on a long car trip at highway speeds I’ll usually leave the windows down unless it’s really hot or there is someone in the car I want to talk to. Then I’ll cycle the A/C on and off to keep the temperature moderated while the windows are up. In the winter I do the same with the heat - I don’t leave it on constantly, but will cycle it on and off to stay comfortable, but to reduce the energy demands of my car.
As for the second part of your question: air conditioners USED to use chlorofluorocarbons (CFCs) but production of CFCs was stopped in the in the mid-90s because they are ozone depleters. It is still legal to continue to recycle and use existing stockpiles of CFCs, however, and cars that were produced prior to 1995 may continue to use CFCs. All new cars after 1995 use HFC-134a, a non-ozone depleting refrigerant. If you have an older car you can check under your hood to find out what kind of a system you have: there should be a label on your A/C. If your car requires CFCs, you can follow one of three options to avoid putting more CFCs into your car: 1. maintain your A/C so it never develops a leak and this is a non-issue, 2. retrofit your A/C to use HFC-134a, a non-ozone depleting refrigerant, which may cost hundreds of dollars, or 3. if you’ve already got a leaky A/C, don’t repair and recharge it. learn to love no-A/C and take yourself out of the equation.
The EPA has more information than you ever dreamed of regarding motor vehicle air conditioning here.
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9 Comments
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i like to drive with my sun roof open … i wonder how that affects the gas mileage. a/c just bothers me … so artificial. BUT, i will use it on those crazy hot days or if i need to arrive somewhere without wind blown hair.
sometimes I really wish I had a sunroof! all of the blowsy with none of the road debris flying through my window and hitting me in the face.
In Texas, we gotta use the A/C. I love driving with the windows down, weather permitting.
I am not efficient. But we are carpooling as much as possible!
there are times and places for A/C! I’m guilty of putting it on for a couple of minutes just to cool off the car when I start driving.
yay carpooling!
I am one of those who took myself out of the equation. I drive a 30 year old car and I do everything I can to keep it safe and driveable. I had a professional mechanic disconnect my A/C and I never looked back.
I am a firm believer in making do with what I have, but also taking care of what I have and taking responsibility. People often tell me to get a new car, but I have to wonder what happens to all the old cars nobody wants anymore? Just today I passed my emissions test, and it’s important to me that I keep my car running as clean as I can so I can keep what I have.
rock on, Roxanne! congrats for passing your emissions test with a 30 year old car. and your car is SO COOL, too!
PS- If you ever find out what happens to all the old cars nobody wants any more, please let me know.
[...] Tiny Choices Q&A: Car Windows: up or down? [...]
[...] debunked here. Check it out! For example, the myths debunk the A/C vs. windows open issue that we’ve talked about here before - “Opening the windows at 65 mph had negligible effects.” [...]