The cassette has the purpose to change the construction of an open to a closed fireplace without its dismantling. It increases the thermal energy and the security of the fireplace as it avoids the direct contact with fire. A cassette also works for new fireplaces while the ventilation system is used for the heating of the neighbour rooms. (Attention: the ventilators of the cassettes don't replace the hot air distribution inside the building). Similary to the insert, the cassette also has a cast-iron corpus that aborbses the heat out of the flames and emits it to the surrounding air. Additionally the heat is emited through the windowpane. Inside the cassette the corpus is locked in a sheet-steal case and the circulation of hot air takes place in the gap between the corpus and the case. The air is induced by two ventilators at the bottom of the front part of the cassette and released through the gaps at the top. Additionally two exits at the top of the cassette are supposed to be used for the hot air distribution in other rooms.

The cassettes have an integrated security system to protect them from overheating. The ventilators of the system switch on automatically when the temperature of the corpus reaches 60ºC. The speed regulation cannot be switched off. The insert is made out of cast-iron, a material that accumulates and emits the heat during a very long period of time. The insert absorbes the heat out of the flames and heats up the air that surrounds the corpus (convection). One part of the heat is emitted through the windowpane. The thermal energy of an insert is about 60-70%, while for open fireplaces it is only 15-20%. Thus the effectiveness of the insert is 4 times higher than of the cassettes. Additionally it saves money for wood, transport, storage and for removing the ash.