I generally run the wood stoves fan throughout the night. Before bed I close the flapper so it's barley open. On my stove I can actually see the flapper so I know its precise position. Waking up in the night to do what most men need to do as they age, I also check the stove. The flapper is always open more than it was where I initially set it before bed. Im guessing the stove is calling for heat as the fan is cooling it down, so it opens up some? If so, this obviously cuts down on the burn time as more wood is being consumed.