I know three friends that have out door wood furnaces, they all use between 12 and 15 full cord per year, they cut pieces longer so the cutting splitting is diminished from standard size wood, however the amount of moving the wood is significantly more than any other form or wood heat, from years past. The neighbors classic, has problems two times a year with a pump going bad, and most famously with the draft door sticking open from the servo motor going bad or being stuck open by creosote, which causes the furnace to over heat and blow steam 50 feet in the air. Two times I have stopped and helped put out fires that it has created in his wood pile when he is gone to work, from embers blowing off the smoke stack, he keeps his wood pile on the east of his furnace and the wind blows embers or sparks off the chimney or out the front door and caused two separate ground fires. When the power goes out, the pump stops circulating, they loose heat in the house and the furnace will over heat, when the fire box cools off you have to worry about it freezing. I go and put wood in it or they have family members put wood in it while gone on vacation.
We like to cut wood to heat with, we do not like to cut and haul 15 cord per year.