Depends on your current furnace setup, most run into the cold air return and suck the heat from the coal stove using your furnace blower. other setups have a large plenum fan in the top of the coal stove to move the air.
I designed my own, since I don't have blowers in my current furnace. Heat Jacket on LL Hyfire I
Each application can be unique depending on your situation and where you ductwork is located.