Im a bricky and have built over one hundred chimneys in my day,also heated my home for 25 plus yrs with two fireplaces and also build a camp structure every yr and heat with a small woodburner .lots of good points have been made here but I will start at what I feel are problems.first off is the size of the fire box in relation to the diameter of the chimney flue\as well as the design of the smoke shelf,if in doubt always use a 8 in diameter pipe..Next potencial problem is draft,as someone mentioned the top of the stove pipe should be at least 2 ft ubove the roof peak if its closer thand 8 ft to it.Next problem area is damp wood.Ive seen many rookies cutting up deadfall off the ground because it looks dry-it is not,wood absorbs moisture off the ground and it will be too wet to burn clean.Alway reach into a stove with a rolled up newspaper and preheat the flue to establish draft on light-up,hot air rises and this will help with smoke bellowing out the door until draft is going.Also clean you fire box regularly as ash will build up and sometime when wood is pushed into the box the old ash can partially obstruct the exhaust pipe.hope this helps takla