Why is my wood stove smoking?
Wood stoves only smoke when there is not an adequate draft in the
chimney to take the smoke up and out of the stove. The most common
cause of bad draft is a plugged spark spark arrestor (the screen that
surrounds the chimney cap and stops large sparks from landing on
the roof or ground and starting a fire).
 
Here in the foothills and mountains of the Sierras, all chimneys
should be  equipped with a spark arrestor for safety. Once the spark
arrestor gets dirty, the chimney accumulates creosote and soon
there is no place for the smoke to go, but back into the room. Another
cause of smoking, when the stove is first started, is the lack of enough
heat being generated to start the draft. The chimney is full of heavy,
cold air and needs a large burst of heat to reverse the draft and let the
smoke rise.