gaw wrote:I dont have an EFM, but that should not make a difference. My damper hangs open about a third of the way almost constantly at this time of year. When the stoker runs it will do a little flutter when the blower first starts, as if you were to bump it closed with the flick of a finger, but it quickly returns to its partially open position. At times it may move back and forth but never fast, its just a smooth motion. The only time it shuts quickly is when I open the ash door or open the fire door because this breaks the draft. I am using a Fields RC.
That is how it should work, when the fan starts, the firebox will go to positive pressure initially and then return to a negative draft as the chimney catches up to the increased air flow.