I just had my first backfire tonight.
It was supposed to be a warm day today (50 degrees) so I only did a small fire this morning (5:30am) for my wife, it was in the 30's most of the day and felt like it was getting warmer this evening. She said she added a little wood to it around 3pm since there were only very few coals left in it and it was getting a little chilly. By the time I got the kids to bed at around 8 I loaded in about a 60% capacity load, waited til it was well lit (15-20 minutes) and the stove top temperature was about 400 degrees before lowering the air to about 1/3 and closing the bypass.
I watched the temps and slowly closed the air down all the way over the next half hour or so and it was hovering around 500 degrees every time I looked until I was getting ready for bed. So around 11pm I'm getting ready to go to bed and glance at the stove on my way by and it's at 570 degrees and I hear POOF, thinking that's weird I go around locking doors and turning off lights and realize I can smell smoke.
Just like I do when anything "weird" happens I come on here and then google to see what people suggest I do. I opened they bypass because the temperature had quickly risen to 600 degrees in a matter of a few minutes and give it a little air since it was closed all the way.
It quickly cooled down to 570ish before I closed the bypass again and left the air open a crack.
I think the weather may have played a role, it got very breezy and much warmer as the night went on, it's like 51 degrees in the middle of the night in December!
Here's what I read about backfires somewhere else, I especially like the part about seasoning your wood for 10 days:
"It happens because it's very smokey in the
stove so you probably have the flue shut down. Simply open the flue some so you have a better flame rather then a smolder so it burns cleaner. Also have your chimney serviced at least once a year, try to burn seasoned wood (dry). Remember if you split green wood bring it in the garage 10 days later or so most of it's moisture content is gone and it's ready to burn."