I'm just curious what the most energy efficient "medium" setting. On days where it's too warm to leave it off, but not hot enough to require cranking it to the max, what middle-ground setting would be the most energy efficient? It has High, Medium, Low, and numbers 1 through 11. Should I go with High 1, Medium 5 or 6, or Low 11? Or would they all be about the same as far as energy usage? Also, should the "Exhaust" be set to "Open" or "Closed"?