Which consumes more fuel in summer: driving with windows down or using air conditioning?
3 Answers
On urban roads, using air conditioning obviously consumes more fuel than driving with windows down. However, on highways at 70 km/h, the fuel consumption between driving with windows down and using air conditioning is the closest. Below 70 km/h, driving with windows down saves slightly more fuel, while above 70 km/h, driving with windows down consumes more fuel. Adjusting air conditioning temperature: Setting the air conditioning to 25 degrees Celsius is most suitable. One major reason for high fuel consumption in summer is the excessive use of car air conditioning. Therefore, reducing the fuel consumption caused by the air conditioning will lower the vehicle's actual fuel consumption. Avoid prolonged use of air conditioning: Prolonged use of air conditioning increases the engine's load and also raises fuel consumption. After entering the car, owners can first open the windows to let out the hot air inside, then turn on the air conditioning. Periodically adjust the air conditioning settings to prevent it from always operating at high levels.
I paid special attention to this issue when driving long distances on the highway before. Both opening windows and using air conditioning affect fuel consumption, but the key factor is speed. At high speeds, such as over 80 km/h, opening windows significantly increases wind resistance, forcing the engine to work 10-20% harder and consume more fuel—making it less efficient than using AC at that point. When the AC is on, it directly diverts power from the engine, increasing fuel consumption, but the impact is slightly less than wind resistance. In city driving at lower speeds, open windows create less drag and may save some fuel, whereas AC usage consumes more. The bottom line: on highways, closing windows and using AC is more economical, while at low speeds, open windows for ventilation save a bit. Remember to ventilate the car before turning on the AC in hot weather—it reduces the AC load and improves efficiency.
From a physical perspective, opening windows disrupts the car's aerodynamic shape, increasing air resistance and forcing the engine to output more power to compensate, leading to significantly higher fuel consumption, especially at high speeds. Air conditioning relies on the compressor, which consumes engine power and also increases fuel consumption, but in a relatively stable manner. Both methods consume fuel, but opening windows at high speeds is more severe because air resistance grows nonlinearly. At low speeds, window opening has less impact, while air conditioning becomes the main fuel consumer. When speed exceeds 60 km/h, it's better to close the windows and use air conditioning. In city traffic jams, slightly open windows for ventilation but avoid fully opening them to prevent dust and noise interference. It's best to use actual test data—for example, I measured that opening windows on highways increases fuel consumption by 15%, which is 5% more than using air conditioning. Regularly checking tire pressure is recommended to reduce overall fuel consumption and make driving more economical.
