Does a car consume more fuel with the A/C ON or windows rolled down?

This is a question that kept us scratching our heads at least once every road trip. A very similar question was posted on question-answer website Quora. We answered it and decided to have it posted here as well. Updates on the question can be followed by clicking here.

Getting started, both the conditions — running your air conditioner and having windows rolled down can increase your vehicle’s fuel consumption. But “Which among the two is better and when?” is what we are going to discuss today.

Walking you through it

With your air conditioner turned on and running, you push your engine to work harder and not compromise on it’s operations but also run the air conditioner compressor to fulfill in-cabin requirements. Naturally, it burns more juice.

Cars are designed to direct the air coming against them on and around (which is what aerodynamics is all about). When your windows are rolled down, air not only goes on and around, but also enters the cabin and is blocked by the other end. So, your car experiences more resistance by wind or ‘drag’ and has to work more again to not compromise on it’s operation and vehicle speed, eventually drinks more fuel in the process.

The Verdict

Whether you’re burning more fuel with ar conditioner running or windows rolled down depends on a major parameter called “vehicle speed”. Usually, the principles and effects of aerodynamics start to play when your car acquires a certain speed. This speed is close to 80 kmph or 50 mph.

Now above the 80kmph speed, having your windows rolled down can have a worse effect on your fuel economy than using your air conditioner. You’re subjecting your car to higher wind resistance when it is easier for the car to use the same incoming air to cool your cabin.

Below the 80 kmph speed, theoretically, having your windows rolled down can have a better effect on your fuel economy than using your air conditioner. Wind resistance experienced by your car is easier to overcome than having to produce more energy to support the air conditioner as well.

So, to sum things up. Here’s a small table. Do feel free to share this article with friends who may have the same questions. Remember, every drop of fuel counts, as evidently taught by our country’s fuel prices.

To record the results in a table, for the engineers.

Speed

Fuel economy with A/C turned ON (1)

Fuel economy with windows rolled down (2)

< 80 kmph

Worse

Better than (1)

> 80 kmph

Better than (2)

Worse