We've been heating our old western Minnesota prairie house for over a year with a central wood boiler which sits in our back yard. The company is called Central Boiler. They also make a nice line of gas stoves. We're considering buying a gas stove as a back up. Here's a link.
http://www.centralfireplace.com/conews.html Otherwise you might be able to plumb in some additional baseboard radiant units to give you some more heat where you need it. They made a world of difference in our old house.

M22's, VP150, QS4's, HK 630, HSU VTF3-MKII