The 1/4" bolt with two nuts that holds the observation door should be adjusted to allow the cover to hang freely (do NOT secure the cover tightly) so that at 'idle', the door will hang vertically about 1/4" open all around the frame between the door and boiler. When the boiler calls for heat, the vacuum the blower fan creates sucks the door tightly to the opening and air is drawn through the base, up through the fire and then the boiler, then out to exhaust (fly ash drops out through cove and back to the ash bucket. Soooooooo, if you are one of those guys who likes everything up tight and out of sight, you lose! It confounds most folks who see it in operation, however it is brilliant in it's simplicity. I have never had anyone say anything nice about the appearance of an AA, BUT as an efficient bulletproof BTU beast, it is a winner...as you know. Most people think they are popcorn makers..oh well, let them buy Propane, Oil and NG.......or keep stokin' those 15 cords into the OWB!