it is a characteristic of most bituminous coals such as those in nova scotia that have a high/mid volitile content to produce smoke and soot, it's just the way it is. what seems to be the problem however is the you are now experiencing smoke not going up the chimney but rather coming back out the loading door correct?? it is likely that the chimney itself has an obstruction, the pipe leading to the chimney or the baffels withing the appliance itself have accumulated either soot, flyash or both; either way it would appear that you're not getting enough draft to keep the smoke in the appliance and the chimney. how warm is it outside at your location??? if it's aproaching 50º F many chimneys especially short/exterior ones will not draft well. my advice would be to let the fire go out, clean the heat exchanger of the appliance itself, and see what you find, also take all chimney pipe apart, inspect and clean, also put a ladder up to the chimney, get yourself a chunk of lead, a rope and a chimney brush and drop it down the chimney, pull up and repeat many times, use a flashlight to varify nothing such as a dead animal, or collapsed flue tile has plugged the chimney. and if you have a chimney cap, screen, top etc. GET RID OF IT, they are nothing but a hassel and in many cases appreciably reduce draft.