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Does the AC Really Waste Gas? Rolling the Windows Down vs. Blasting Air Conditioning

By Wes Schwengels, May 3, 2018

Gas prices are up, and soon the high temperatures will be, as well. We all know that cruising with the windows down or the air conditioning on hurts a car’s gas mileage. But which one is worse for your fuel economy — and thus your wallet?

ac windows

The best choice, MPG-wise, is to sweat it out with windows up and AC off, but that’s not always an option, of course. If you have to choose, in general, running your air conditioner will use more gas than having the windows down.

Speed matters

Having the windows open while you drive creates aerodynamic drag on your car, and that drag increases as you go faster. Still, a 2013 Society of Automotive Engineers study found that, compared to having the AC on instead, this drag wastes less fuel until you hit about 75 mph. 

So, if you’re cruising along on the freeway, you might be better off with the air conditioner on. But in most conditions, rolling down the windows will be smarter for your bank account.

Why the AC guzzles gas

Why is the AC so bad for your fuel mileage? The energy needed to run the air conditioning compressor requires your engine to use more gas. And the hotter it is and slower you go, the greater the drain.

In fact, the U.S. Department of Energy found that running the AC in hot conditions can reduce your gas mileage by more than 25%. That’s quite a hit.

Tips for using the AC efficiently

But sometimes you just need that cold air. Driving with the windows down when it’s 105 outside won’t bring much relief. With that in mind, here are some tips for using your AC wisely.

  • Leave your windows down a crack or use a sunshade when you park. The less heat that bakes into your car while it’s off, the quicker it’ll be to cool down.
  • When you’re ready to start your car, let as much hot air out as possible before turning on the AC. Roll the windows down or keep the door open before putting it in gear to let the temperature come down.
  • Don’t start the air conditioning until you’re moving. Running the AC at idle won’t do you as much good, and will waste even more fuel.
  • Only set the AC as cool as you need it to feel comfortable. Sure, it can be satisfying to crank it full blast, but that satisfaction will disappear when you start having to fill up more often.

And there are other ways to save gas, too. From maintaining proper tire air pressure to keeping up on scheduled maintenance, you can find more tips here.

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