Do Car Air Conditioners Burn More Gas?
There have been multiple debates on which method of vehicle cooling is more fuel efficient: air conditioning or driving with the windows down. There is no doubt both cause more fuel to be burned. The question is, which burns more?
| Cooling Method | How It Affects Fuel Efficiency |
|---|---|
| A/C on | Burns fuel to run the compressor |
| Windows down | Increases aerodynamic drag, especially at higher speeds |
Open windows increase drag while driving, and running the A/C burns fuel to run. Eager to prove conclusively which option had greater impact on overall miles-per-gallon (mpg), the Society of Automotive Engineers (SAE) and General Motors conducted a controlled study comparing the fuel efficiency of driving with the car air conditioner on to driving with the windows down.
Driving With Your Windows Down
After comparing cars at speeds of 31, 50, and 68 mph in 86°F weather, they concluded:
| Finding | Result |
|---|---|
| Driving with windows down | More fuel efficient than running the A/C |
| Closed windows and no A/C | Significantly better on fuel than either option |
When to Roll Down the Windows
| Speed | Recommendation |
|---|---|
| City driving (under 40 mph) | Windows down is generally more efficient |
| Highway driving (over 55 mph) | A/C may be more efficient due to reduced drag |
| Extremely hot conditions | Difference may be minimal—comfort may take priority |
Pro tip: Follow these directions to recharge your car’s air conditioner.
Extreme Weather Temperatures
So if you need to cool off during a hot summer drive, consider rolling the windows down. Though some experts say A/C is the wiser option for fuel economy, multiple tests have shown otherwise. But the difference does not appear to be as great when conditions are not extremely hot.
| Condition | Effect on Fuel Economy |
|---|---|
| Mild weather | Difference between windows down and A/C is minimal |
| Extreme heat | A/C works harder; fuel efficiency drops more noticeably |
| Stop-and-go traffic | A/C efficiency decreases further |
Additional Reasons to Limit A/C Use
Engine Overheating Risk
“In front of the radiator is the AC condenser which is very hot, often over 250 degrees,” says Chris “Moose” Pyle, a master-certified technician with JustAnswer. “So you are pulling extremely hot air through the radiator and into the engine compartment with the fan.”
| Situation | Risk |
|---|---|
| Older or poorly maintained cars | Higher risk of overheating with A/C on |
| Stop-and-go traffic | Reduced airflow; A/C works harder |
| Mountain driving | Extra strain on engine and cooling system |
Environmental Impact
Using your car’s A/C also contributes to higher fuel consumption, which means more emissions. Reducing A/C use even a few days a week can make a small but meaningful difference.
Does the Outside Temperature Affect AC Efficiency?
Yes. The warmer the outside temperature, the harder your AC system will have to work to keep you cool.
