For what it’s worth, we’ve put in an Invicta 14kw cast iron stove (Preston), to heat about 125 m3 space two storey open area, and probably heats more than that. Stick with cast iron as it holds the heat. We use 50 cm cut wood, so that sets a size limit. Properly installed with new flue in an existing chimney (unit went into a fireplace so required extra work), including the local company coming round and commissioning the stove. No complaints.
We bought an Invicta Samara poele a bois back in July and installed it in September after a couple of people recommended Invicta’s. It’s in a room approx 90m3 and seemed ok, but real test will be our next visit in December.
We have a 14kW Invicta installed and it is superb. Bought at the local Brico and the price was acceptable when compared to others. Totally satisfied and could recommend them.