Reply:  Do not open the door before the wood is burned all the way down to embers. When opening the door, a lot of cold air will get in contact with the flames which may cause smoke inconveniences. If you for some reason have to open the door before the wood is burned to embers, this has to be done carefully. Let the door stand on a 2cm gap for a moment before opening it completely. Another reason might be poor draft conditions. A chimney sweeper is able to measure the draft.
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