The contra-flow system is used to collect thermal energy from hot flue gases. When wood burns in the firebox high temperatures are reached quickly, forcing the burning flue gases into the upper combustion chamber below the top lid. The hot gases are then guided down and out into the side channels, where the heat is released into the exterior stones. At the same time, room air outside the fireplace walls warms and moves up the stone surface in a path opposite to the interior downflow. These two opposing air flows are known as contra-flow. Most of the generated heat is transferred evenly into the room in the form of comfortable radiant heat.
Firewood burns quickly and efficiently in the firebox and the solid mass of the Tulikivi rapidly stores the heat. A couple of loads of wood are sufficient to heat any room, and heat will be radiated up to 24 hours or more.
A Tulikivi fireplace does not waste heat or wood like a normal stove or open fireplace, which have to be continually fed to keep the fire burning.
Tulikivi fireplaces can be equipped with an outside air kit, e.g. in passive energy houses. An air duct guides combustion air from outside directly into the combustion chamber. Models of fireplace groups 1 and 2 require an additional adapter, whereas group 3 models can be connected without an adapter.