Does it actually make a difference in mileage? My assumption would be the difference is just an "open" vs "closed" venting state. I suppose "open" could increase drag somehow, depending on how it was implemented... Admittedly using AC/heat, or even just the fan, vs not using is a choice people make based on personal preference vs mileage--I'm mostly comfy with windows/roof open when it's hot out and if I need more than that I can pop on the AC for a bit.. and winter unless I'm unusually cold or need to defog/frost my windshield I mostly figure I'm good as long as I'm out of the wind, hehe. So I don't have the fan on in my car most of the time because I think it's unnecessary. But recirc power usage, I can't imagine there would be any. In fact I think it's kind of foolish that they didn't have an extra condition for the recirc being on automatically, namely that the fan should be on. I do turn mine to recirc sometimes for particularly stinky circumstances, but otherwise why on earth would I want to have trapped air in warm weather if I'm not using the AC? Recirc doesn't dehumidify, AC does. Recirc by itself is mostly dumb as far as I'm concerned, except specific (as I said, stinky) circumstances (exhaust, skunk, etc).