How do you know if the flue is open?

if it is instaled corectly, the handle which controlls the flue goes in the same direction as the plate inside the chimney. so if the handle is horizontal, the flue is closed. if the handle is verticle, the flue is open. you shouldn't have to close the flue all the way, at most it should be at a 60degree angle to allow smoke to leave, while retaining heat. open the flue all the way when you open the door to the stove so that the smoke will go out the chimney and not into your face and house. but close the flue back down some to keep in the heat and not waste firewood warmth on the air outside.