Think Turning Off A/C In Your Car And Opening Your Windows Saves Fuel - Think Again!

Opening car windows may do more to reduce a vehicle's fuel efficiency than turning on the air conditioner.

Some drivers will try and lower their fuel consumption by opening their car windows instead of cranking up the car's air-conditioning unit. That may not be the answer to maximizing fuel economy, however, says SAE International. It all depends on speed and traffic conditions, as well as how long the car has been heating up.


Without a doubt, air-conditioning is "one of the highest energy consuming accessories" a car has, and its effect on fuel economy varies, depending on how fast the car is going, outside humidity, and traffic patterns. For instance, in some cases, the impact of open windows may bring down fuel economy faster than running the AC because they increase a vehicle's aerodynamic drag.

In general, using recirculated air for the AC system is more energy efficient than pulling in outside air but, again, it all depends on the conditions. For example, running AC at full blast can cut the fuel economy of a vehicle traveling at 30 miles per hour by as much as nine miles per gallon. The report suggests first opening the window to cool down a heat-soaked car, then moving to the AC blower. It can be complicated.
In the summer sun, a car heats up a lot faster than a house does, according to the SAE. During a 94-degree day, a single-story house that starts the day with an interior temperature of about 70 degrees can add as much as 10 degrees Fahrenheit of heat. In the car? That temperature can surge as much as 70 degrees. In fact, the surface of a car seat can reach 130 degrees Fahrenheit by late afternoon, while the top of a vehicle's instrument panel may reach more than 200 degrees. Whether you use AC or an open window, something needs to be done about that heat.