I accidentally do this a couple times every Summer. I’ve already done it once so far this Summer, and the worst of it was that it wasn’t even a very hot day. Whereas a day like yesterday I wouldn’t have minded it much if I accidentally left my a/c on. I think my electricity bill is pretty reasonable even during the Summer because I don’t turn my a/c on that high, and it’s only on mostly during the weekends. The only other time of the year my electricity bill gets noticeably higher is when I’m leaving my computer on during all hours of the day because I’m downloading very large batch torrents.