Got any idea how the place was heated in its prime? That should give you a clue as to what direction you should be headed. I think begreen is pointing you in the right direction. Check out the boiler room forum here on hearth.com, they spend time talking about hot air furnaces along with boiler systems. Tall stacks and large spaces are not something I have experience with, so will get out of the way. Good luck and keep us posted as to how you are getting along with any changes you make. Really unique and fascinating space you are working with. I'm sure you can heat that place, the question is, can you afford it?