I dunno it was crazy. I heard a rumble for 2 seconds looked at the cookstove and a good sized puff of smoke came out of the cooktop and chimney areas like a backpuff does then sucked back in and ignited like an explosion in reverse going in an up the flue it charred the fluffy creosote on the damper grates so they cherried. . . Was this a backpuff a split second before the wood I had put in ignited that ignited the backpuff smoke? . .