All the 7900 stoves can be fitted with extra heat storage in the top. You can choose between a low top that can accommodate 30 kg of heat-storing stones and a high top that has room for up to an entire 95 kg of heat-storing stones.
It means that the stove can give off heat for many hours after it was last lit. The fire's output can thus be exploited by accumulating the heat produced in the environmentally-friendly combustion chamber in the heat-storing stones in the top. The top module can also be purchased on its own to make a higher stove - up to 182 cm, so you are reminded somewhat of the old French heating stoves.