I'm going to vote for "none of the above". If you have unfinished space in the basement and a reasonable ability to get to it from outside, my vote is to put the boiler in the basement. Especially with the jacket off, you can change the whole feel of the house by gradually heating it from below. At the same time, you can protect your fuel supply against freezing by keeping it a basement bin, and you don't have to trudge out to the garage at 3 am if you happen to blow a shear pin. And with minimal attention and effort you should not have any problems with coal dust or ash.
We have a bird, a cockatiel, and burn truckload quantities of coal each year. The bird likes the extra warmth we put in our living space and has never uttered a single peep about dust. Without coal, we might have to trade her for a penguin.
Seriously, even though my SO didn't like the oil bills, she was pretty skeptical about coal before we started. That ended about halfway into our first day on coal heat. Since then she has volunteered to tend stoker stoves, and for a year served as Chief Wheelbarrow Operator to supply coal to our current boiler. She's very much a pacifist, but I would not want to be the person who proposes to her that our coal boiler be moved to an outbuilding.