I haven't been able to find a satisfactory answer. What would save the most electricity? One of my roomates and some of the neighbors below us think that it is better to leave the air conditioner on all day. Normally, for just one house with one air conditioner, I would be very skeptical: I am more convinced by this explanation here: http://michaelbluejay.com/electricity/cooling.html My neighbor brings up an interesting point that I didn't consider: that we have two floors. He says, "Like it or not we all share the same house. If we turn off our air when we're not home, your air has to work twice as hard to stop our hot air from displacing it. Since we don't all live on the same schedule, we're going to end up causing each other's floors to work harder than they have to." How does this change the dynamic, with the 2 ACs out of sync? Ideally, we would have programmable thermostats, but we don't. In addition, there is the issue of moisture, and how long it takes the air conditioner to "warm up." This website (http://www.srpnet.com/energy/ask/air.aspx) says it takes an AC 7-10 min. to reach max efficiency and recommends leaving the AC on due to moisture. Now that it's Fall, AC doesn't matter as much, but I am very interested in finding out the truth. Edit Sorry! Wrong Forum! I made a new thread in General. Feel free to delete this one.