Useful Car Tips

Fuel Efficiency: Windows Down or AC On?

August 14, 2019
It’s important to stay cool under the sun this summer, especially with a series of temperature records being broken across the globe. Depending on geographic location, summer temperatures can range anywhere from the mid-70s, soaring all the way to the high-90s and and beyond; temperatures that no one wants to endure in their car without some assistance. Of course, we have two main solutions when we’re traveling in our cars this summer: opening up the windows or turning on the air conditioner. Personal preference plays a role in selecting the optimal option, with some preferring the cooling blow of the wind, with others preferring the gentle circulation that a good air conditioning unit provides. Besides subjective preferences, are there any objective factors to consider when choosing between the two? The answer is simple: fuel efficiency! Fuel efficiency differences may seem minimal at first, but can quickly add up, especially during long road trips when traveling to your favorite summer destinations. For those looking to save a little money this summer, it’s important to know the differences and adjust accordingly. Let’s take a look at the differences between these two methods for keeping cool to find which one will ultimately prove to be more fuel efficient for your needs.


Driving with your windows down introduces fresh air into the interior and can keep it from feeling too humid inside. When driving at high speeds, such as on the highway, the wind can cool you down. Some don’t like driving with the windows down as it can lead to uncomfortable loudness or buffeting, especially when driving at higher speeds. However, how well does this method of cooling work in terms of fuel efficiency? The answer is complicated. While driving with your windows down introduces fresh air into the interior, it also introduces higher drag, the resistance all moving objects (including your vehicle) encounter when moving through the air. While modern vehicles are designed with fuel efficiency in mind, with aerodynamic shapes to cut through the air and reduce drag, rolling your windows down increases the drag exerted upon your vehicle. A complicating factor is the form factor of your vehicle: if you drive an SUV or truck, your vehicle already experiences more drag than others on the road. Thus, rolling your windows down is unlikely to drastically affect drag. Conversely, a low drag vehicle such as a sports car may encounter an increased proportion of drag as compared to an SUV or truck.


Just as driving with your windows down has its drawbacks in terms of fuel efficiency, driving with the air conditioning on isn’t a perfect method either. Turning on the AC uses more fuel to run as an extra load is applied to the engine. The hotter it is outside (such as during heat waves), the harder the air conditioning system needs to work. The form factor of your vehicle again becomes an important factor when using AC. If you’re driving a sedan, it may be a better idea to shut the windows and turn on the AC when traveling at very high speeds, as this is when the drag of open windows will likely make AC the more fuel efficient option. Although driving with your windows down can, in some circumstances, be more fuel efficient than driving with the air conditioning on, this simply isn’t bearable for everyone. The noise may cause undue discomfort and potentially wear a driver down when traveling on longer journeys.


With so many contributing factors to this issue of fuel efficiency, here’s a general rule of thumb to follow: Keep the windows down while traveling in the city and turn on air conditioning on the highway. As mentioned before, this is because every vehicle has a different speed at which rolled down windows cause so much drag so as to decrease fuel efficiency versus AC. This information is supported by a 2004 study by the SAE (formerly the Society of Automotive Engineers) which suggested running the AC will likely result in worse fuel efficiency than driving with your windows down. To save a little money on gas this year, try not to use the AC more than necessary or set the temperature lower than necessary. Before turning on the AC, open or drive with the windows for a short time before turning it on, as doing so will help dispel hot air. Finally, consider parking in the shade when available and use a Fortem sunshade when it’s hot. Follow these tips, consider the pros and cons of driving with your windows down versus turning on the AC, and you’ll be well on your way to gas savings this summer and beyond!
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