My sunroom would suck heat out of the house all night long when i used to keep the door open in winter. I was shocked at how much less fuel i used when i started closing the door at night. I swear it took 3 times more heat at night than it gave during the day and it gives a lot during sunny days.Good idea on the sunroom, but it is a part of our kitchen with a breakfast bar pass through, not really feasible. Maybe I can think up some way of measuring if the 3rd zone in the sunroom is kicking on or not.