Is it more 'engergy efficient' to turn the thermostat up when I leave?

Question

Is it more energy efficient to turn the thermostat up to 85 when I leave the house or leave it at 75-78? I personally think it takes more energy for the AC to cool the warm air when I get home rather than just maintaining a static temperature when I'm gone, but my roommates disagree. Any educated insight?

Answer 1

By turning the thermostat up from 78 to 85 on a 100 degree day, you've decreased the indoor/outdoor temperature difference from 22 degrees to 15 degrees.  In theory, you should use about 1/3 less energy to cool the house.    

But with the inconvenience of having to turn it back on and wait for the house to cool down, plus the uncomfortable swings in indoor humidity, it probably only makes sense to do it if no one's going to be home for a lengthy amount of time, e.g., 6 or more hours.

On the other hand, if you live in a newer, well-insulated house and have relatively low utility bills you could leave the thermostat lower and not worry about it.

Answer 2

I was told that it is more efficient and less hard on your AC unit to just turn the thermostat up than to completely turn the system off.

It actually takes more energy to recool or heat the house from scratch by turning on the machine, so leave that baby on!!