Narvi Stone CageStone Cage, Black, 250x400 With the aid of a stone cage, the heat of the flue can be utilized better. The steam lasts longer when the sauna water flows from the stone cage to the stones. With the aid of a stone cage, the heat of the flue can be utilized better. The steam lasts longer when the sauna water flows from the stone cage to the stones of the sauna heater. This is also a way of decreasing protective distances into flammable material. Stone