Turning Off Your Car's A/C Can Save Gas, But There's A Catch

Running your car’s A/C can burn more fuel, but rolling down the windows is not always better. Here's what drivers need to know.

Mercedes-Benz MBUX Hyperscreen Air Vents

Dan Mihalascu

By: Dan Mihalascu

Oct 22, at 7:00am ET

Add Motor1.com as a preferred source in Google

Comment

Turning on your car’s air conditioning makes summer driving more comfortable, but it can also mean more frequent trips to the gas station. The compressor needs energy to cool the cabin, and in a conventional gasoline car, that energy ultimately comes from the engine.

So, does switching off the A/C really save fuel? Yes, but the difference depends on the vehicle, the outside temperature, the length of the journey, and how fast you’re driving. There’s also a catch: opening the windows can increase aerodynamic drag, meaning the most fuel-efficient choice is not always as straightforward as it seems.

Why Does Air Conditioning Use More Fuel?

In a conventional gasoline-powered car, the air-conditioning compressor places an additional load on the engine. The engine must work harder to power it, which means burning more fuel than it would under otherwise similar conditions with the A/C switched off.

The effect becomes more noticeable when the system is working hard to cool a hot cabin. High outdoor temperatures, direct sunlight, and a vehicle that has been sitting in the sun can all increase the cooling demand.

According to Natural Resources Canada, air conditioning can increase fuel consumption by as much as 20% under certain conditions. That figure is not a universal penalty, however; the actual impact varies with the vehicle and its operating conditions.

How To Use Your Car’s A/C Without Wasting Fuel

You don't have to endure a hot cabin to improve fuel economy. A few simple habits can reduce the workload on the air-conditioning system without sacrificing comfort.

Let hot air escape first. Open the doors or windows briefly before setting off to release the heat trapped inside a sun-baked car.
Use recirculation when appropriate. Once the cabin has cooled, recirculating interior air can reduce the amount of hot outside air the system needs to cool.
Choose a comfortable temperature. Setting the system to an extremely low temperature can increase cooling demand unnecessarily.
Close the windows at higher speeds. This helps preserve the car's aerodynamics and allows the A/C to work more effectively.
Park in the shade when possible. A cooler cabin needs less energy to reach a comfortable temperature.
Keep the system maintained. Follow the manufacturer's maintenance recommendations so the air conditioning can operate as intended.

These measures won't eliminate the fuel used by the A/C, but they can reduce the time the system spends working hard.

How Much Fuel Can You Save By Turning It Off?

There is not one percentage that applies to every car. A/C use can have a relatively small effect when the system only needs to maintain a comfortable temperature, but the penalty can be considerably larger when it's working at maximum capacity on a hot day.

Short journeys can be particularly demanding. If a car's interior has become extremely hot while parked, the air conditioner must remove that accumulated heat before it can maintain a comfortable temperature. The journey may end before the cabin has fully cooled, making the energy used for cooling a larger part of the trip's total fuel consumption.

The U.S. Department of Energy has also noted that using A/C in hot weather can reduce fuel economy by more than 25% on short trips in some circumstances. That's a potential worst-case-style figure, not a prediction for every vehicle or journey.

Is It Better To Drive With The Windows Down?

It sounds simple: if air conditioning burns extra fuel, just open the windows instead. At low speeds, that can be a sensible option because open windows generally create less aerodynamic drag than they do at highway speeds.

As the car moves faster, however, air flowing into the cabin disrupts its aerodynamics. The resulting drag forces the engine to use more energy to maintain speed. At highway speeds, that extra resistance can reduce or even erase the fuel savings from switching off the A/C.

A study conducted by Oak Ridge National Laboratory compared air-conditioning use with open-window driving in a 2009 Ford Explorer and a 2009 Toyota Corolla. At cruising speeds between 40 and 70 mph, both vehicles used more fuel with the A/C running at maximum cooling than with the windows open.

But the results varied at higher speeds and between the two vehicles, showing why there is no universal cutoff point. The practical takeaway is straightforward: opening the windows can make sense around town, while using the A/C with the windows closed is often the better choice on faster roads.

What Drivers Say About Air Conditioning And Fuel Economy

Drivers on Reddit have debated whether running the air conditioning noticeably increases fuel consumption. In a discussion on r/cars about whether A/C reduces gas mileage, commenters discussed how the compressor puts extra load on the engine, with some arguing that the fuel penalty is small enough to justify staying comfortable on hot days.

Another common debate is whether it's more efficient to open the windows or run the A/C. In this discussion about air conditioning and fuel use, users considered how driving speed and aerodynamic drag affect the comparison. The general takeaway is that open windows may make sense at lower speeds, while using A/C with the windows closed can be preferable on the highway.

Drivers also point out that results vary between vehicles and driving conditions. A discussion on r/cars about air conditioning in modern cars touches on the difficulty of noticing a consistent mileage difference in everyday driving.

Do Modern Cars Use Less Fuel With The A/C On?

Modern vehicles can manage air conditioning more efficiently than older models, but they don't eliminate the energy cost of cooling the cabin.

Some systems vary compressor output according to cooling demand instead of running continuously at full capacity. Automatic climate control can also regulate the cabin temperature without requiring the driver to keep the system at its coldest setting.

What do you think?

View

Comments

Hybrid vehicles may use electric compressors, allowing the air conditioning to operate even when the gasoline engine temporarily shuts down. However, the electricity still has to come from somewhere, and cooling can affect overall efficiency.

Electric vehicles face a different version of the same problem. They don't burn gasoline to power the A/C, but the system draws electricity from the battery and can reduce driving range. AAA testing has found that cabin heating and cooling can significantly affect EV efficiency, with the size of the impact depending on ambient temperature and operating conditions.