Question: Occasionally I have a phenomena occur with my woodstove. It'll be burning nicely along, with the air intake set for minimum air. I'll add a new log and a couple of minutes later the stove will "puff" smoke out from around the door gaskets. It'll do this two or three times, then settle down and burn properly. The last time it did this I ran outside and checked the chimney. When the stove "puffed" the chimney seemed to put out a whole bunch of smoke as well. Answer: This is known as flashback or delayed ignition and is quite common. You described it quite well. It happens when there is too much fuel for the amount of air present. This causes the fire to look for air and pull draft into the stove very quickly. This causes the fuel (gases) to ignite, however the effect is a mini-explosion which sends smoke puffing out of doors, gaskets, seams and stovepipe joints. For this reason, always be cautious when opening the loading door of a stove that has a large wood charge and limited air. There have been people who have had their eyebrows singed off and even worse then they put their face right up to the stove door and opened it suddenly. There are solution to this situation. One is to open the air control before loading the stove and then run the stove with the air full open for a few moments after inserting the new fuel load. Another is the installation of a barometric draft regulator on the stove smoke pipe. This can stabilize the chimney draft.