Question: I have a Vermont Castings Defiant circa 1986 which I have owned since new. It is located in our 1st floor living room of a 2 story house. It works fine always when the doors are open and also when it is closed down when there is some wind. On 'still' nights the top plate will briefly lift up and emit a large puff of smoke every 5 or 6 minutes. This requires us to open the front doors of the stove or have a very smoky house. The obvious has been done - ie clean chimney and stove dismantled for ash removal annually. To me it seems like a back draft and yet the fire is very hot when this happens. Answer: It sounds more like "delayed wood gas" ignition than a back draft. This is often because the stove air control has been set down too low....the fire is starved for air and finally grabs some from leaks in the stove...causing a mini-explosion in the stove and the release of smoke because of it. Solutions are varied. Make sure the unit is well gasketed. Do not load excess wood...read the hearthnet articles about having a flame on your site. Do not shut the draft all the way. Keep the secondary draft partially open. Also, the installation of a turn damper or barometric damper can help. ---answer #2 Since you've eliminated cleaning issues, three things come to mind: 1) Don't shut the stove down too much at night. Be sure to keep the flue warm as much as possible for a good draft----especially if the main body of chimney is exposed outside. Use your griddle top thermometer as your guide and experiment with various temps. 2) Don't burn wood that's too dry (burns too hot, too fast, shuts down the t-stat). If it's gray in color, mix it in with greener wood. 3) When it "puffs", it's a signal from the flue to send more heat up to reestablish a draft. You as the operator, can overcome many draft inadequacies by determining how much heat should enter the flue. Sometimes you have to sacrifice some heat efficiency for performance. Also: Review some of the information contained in the website on this subject.