1y ago

Which one is more energy/fuel efficient to cool the inside of the car: lower thermostat + lower fan speed, or slightly higher thermostat + higher fan speed?

On a hot day and traveling in a car, which method of keeping the occupants comfortable with the A/C is more energy and fuel efficient?

Set the thermostat to a lower temperature and keep fan speed to the lowest setting
Set the thermostat to a slightly higher temperature and compensate by setting the fan to a higher speed so you can feel cool enough with the breeze

27 comments

Mythbusters did a test on this comparing AC to driving with the windows open. The AC barely affected the fuel consumption, while the additional drag of open windows made a huge difference.
So because the difference between off and full blast is negligible, less than the wind resistance of open windows, I'd say it probably doesn't matter what setting it's on. Go ahead and blast it.
- I thought they found that it only mattered when the car was moving over 45mph that open windows caused enough drag to affect fuel more than AC?
  
  It was. Wind resistances starts picking up at 30mph, becomes an actual factor around 40, and by 50mph makes a pretty huge difference.
  It also depends on your car and what windows are open and how much. American cars tend to be pretty good about having the windows rolled down, but my Outback is AWFUL with the windows down at speed.
  
  Aerodynamic drag increases with the square of velocity so the math checks out. Every additional 10mph is going to have a far greater impact than those before.
  
  Honestly, I don't remember all the details. But that would make sense.
- My AC makes a notable difference in fuel mileage, even taking into account, the fact of gasoline density between summer and winter
  Like, just forgetting I have my defroster on in the winter now makes a notable difference in how much fuel it takes compared to just the arms and legs setting
- He asked about fan speed, not open windows.
  
  Right, my point was that having the air on at full blast was negligible, barely affecting the efficiency of the car. So the settings probably don't matter very much.

27 comments