It's a cross between rocket science and brain surgery - I like to mix my metaphors Efficiency does not always mean fuel economy; consider the stress on the part itself of always being on If having something on 22 means it isn't cold enough, put it on 20! Just because the number is 20, who cares... it is about the level of comfort I now have a VW Jetta and setting it to 22 makes it cool, whereas in the Falcon 22 seemed warmer... at the end of the day the number is irrelevent, it is how you feel. I'd be shocked if you set it to LOW and it still wasn't cold enough on anything but a 45 degree day