This is the system I came across that heats central heating as well as direct output.

At 10kw it may not be sufficient on its own and I imagine you would need another source of heating for the property as well. May be another pellet stove or two of these stove boiler combos. I wonder if they can be run in series?

They attract a £1500 grant compared with £600 for a normal pellet stoves.

I wouldn't rule out the ducting just yet as knocking holes in a corner of a room behind where the stove will be placed and run a duct under the floor to other rooms is less work and cost than putting in radiators.

What is the building made of? Timber frame with block?

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Stuart