Now that summer is finally here, it’s time to clear up some misconceptions around driving with the windows down versus using the AC to cool down your car.

Is it more energy efficient to use the A/C or to roll down the windows?

Increasing Fuel Efficiency While Driving

Using a car’s AC takes extra energy from the engine, so it requires more fuel to operate. When windows are opened, the car has more drag which slows it down, meaning it needs more fuel to run. Both options require more fuel than driving with the windows up and the A/C turned off; but the speed you’re driving makes a difference in what option is more energy efficient.

Some people think that turning on the AC is the best way to be fuel efficient, however the best option tends to depend on the speed you’re driving. MythBusters Jamie Hyneman and Adam Savage created an experiment to get to the bottom of this question.

The MythBusters filled up two identical cars with five gallons of gasoline each. One car had the AC on and the other had the windows rolled down. Each car was driven at 45 miles per hour around a track until one car ran out of gas.

Eventually, the air-conditioned car stopped, while the car with the windows down continued to run for another 15 miles!

Generally speaking, when you’re driving over 40 mph, use the A/C; turn off A/C and open the windows when driving under 40 mph to maximize your fuel efficiency while driving.

And of course, we encourage you to leave the car parked at home and bike or walk instead when you can, especially for short trips.

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