The timing of the smoke relative to last loading? If it's five to ten minutes after putting 30 to 40 pounds of wood in it, remember you just threw nearly a gallon of water in the woodstove and are boiling that off, and out the chimney.
I have a method, some will like it, some will agree, and some won't. Just as well we all do what we feel is best.
I light the stove, insert, boiler, whatever it is. Some newspaper, kindling, and a few small splits. Touch it off and open the air up all the way. Let it burn down to coals or near, then add a few larger splits... let her burn! When the stove is "nearly hot enough", add two or three larger splits, and keep it open and roaring. Try to get the wood fully burning, on all sides.
When the stove isn't quite as hot as you want, but nearly so, close the air down and damper it.
NOTE: Close the air supply in increments, please. Not everybody has heard the stories apparently about airtight stoves "exploding". It's a real story, and has happened. Go half, then half, than half, to leave time for the fire to equalize and slow itself gradually.
Mechanism is basically a "backdraft", similar to the experience of firemen entering a building where there is a large, smoldering, unvented fire. When it gets air, "BOOM".
Fire is cranking along, hot a hard. Producing heat, which produces gas, which burns in the presence of air. It's hitting on all cylinders, and all the sudden, some dummy cuts off all the air trying to choke it. Well, it's still producing gasses at the same rate, and the stack velocity is still there, so a vacuum is formed in the system. Can't suck the stove in like a milk jug, and the chimney is generally pretty airtight, so it sucks a gulp of air down the chimney. "KABOOM".
Cousin had a customer call in last week and yell at his associate over one. Seems he slammed 'er shut on a roaring fire and went to leave. He didn't get to the door, and the soapstone off the top of the stove was all over the room, and the glass from the door was too...
