I've been using this long enough so I think I know it's capabilities. Shelter 2626 with thermostat controlled forced draft secondary air, and secondary burn chamber. rated at 100,000btus. This stove is identical to the Fire Chief line. Shelter is the name carried at Menards stores.
In the Fargo area, burning North Dakota lignite coal (sub-bituminous), heating 2500sq ft century old farmhouse (including basement).
If the temp is 20+ F I can get 7-8 hrs burn time at 70F indoor temp. Can get 10+ hrs at 65F sleeping temp.
If the temp is -20 to -30 I can get 3.5-4.5 hrs burn time at 70F.
The variations in burn times are related to how windy it is outside.
Achieving these results requires raking the ignited coals forward towards the secondary blower, and banking heavily towards the empty back of the stove. This way I don't drastically lower stove temp by throwing fresh coal on top of hot burning coal.
My guess is with the next two sizes up of this model furnace, some pretty respectable burn times could be achieved. But in my scenario I think I'll stick with what I've got in the basement and just add a parlor stove upstairs so I can run my Shelter cooler in order to get longer burn times.