BlueDuck, the only real simple way to tell if it is the coal would be to buy a few bags of a different brand of coal from a different source.
Then you can use the new coal for a few days and see if it is noticably different.
I have burnt coal from five different sources, and each was different. Sometimes only slight differences, sometime huge differences.
First when you first add new coal to a red-hot bed of coal, does the new coal flame iwth yellow flames and smoke?? Or does it just sit there and crackle and pop like a bowl of 'rice crispies' ?? If it flames yellow it probably Bituminous coal. If it crackles it is anthracite.
I would add the additional height to the chimney. But I'm confused about the smell hanging around outside the house, Do you live in a low spot, or depression where the air stands still or stagnate?? I went outside a few moments ago and stood downwind of my chimney and took a good sniff, and I really can't smell much, And I'm burning a mix of the stinky [at first light-off] Bituminous coal and Anthracite.
I hope you get it figured out, it certainly sounds like you went to extreem measures when you installed the stove.
Maybe this is a personal thing for your sense of smell?? I know I just about gag when I'm downwind of cigarette and cigar smoke, but can stand, even enjoy some pipe smoke?? And I have to use an inhaler after a good whiff of leaves or damp wood burning!! Is it possible you are really sensitive to sulphur smell?
Hey, I just though of something, Do you have any exhaust fans running or other exhausting air sources in your house?? These could be pulling fumes from the small air gaps at the top and bottom of the door glass in the MarkI. This could be the source of the smell!.
Do you have a really 'tight' house that maybe needs an outside air source for the coal stove??
Just a thought. Greg L