Windows up? A/C on?

Dog Out the Window

It’s a hot day, you’ve got a long drive, and your mind is wandering. Ever wondered whether it’s more fuel efficient to drive with windows down or up? Air conditioning on or off? So did I!

For a while, I was under the impression that turning on the car’s AC was bad because it burns extra gasoline. This is true: using AC increases fuel consumption by about 10%. But it’s also true that opening your windows, especially at high speeds, increases the wind resistance on your car, which increases your car’s fuel consumption. At certain speeds, opening your windows also increases your fuel consumption by 10%. So what is the tradeoff here?

As it turns out, the break-point is somewhere between 40 and 45 mph. At 40 mph, it makes more energy sense to roll down the windows, and at 45 mph, it is more sensible to turn on the AC and keep the windows up. This is not to say you should alternate between using the AC and rolling down the windows every time you switch between 40 and 45 mph (that could get pretty tricky and time-consuming), but as a general rule, keep the AC for highway driving, and leave your windows down for everything else.

Photo from flickr user Photography Land and Paolo Rally

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2 thoughts on “Windows up? A/C on?

  1. Joanne Bernot

    Aside from the issue of AC, you should NEVER allow your dog to ride with his/her head hanging out the window! Would you allow your child to ride that way? Dogs should always be restrained in a seat belt harness for their safety and yours.

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