The foundation furnace is not equipped with a heating insert. There is also no additional heating box or ashtray. It is made of chamotte elements and can take on basically any shape, and of course the physical requirements must be respected to ensure clean and economical combustion. This means m.in., that air openings for combustion, made in the furnace door, must ensure a sufficient supply of air. The combustion chamber should be large enough, to accommodate the amount of wood correct for the size of the stove. Lengths and diameters of smoke ducts and the number of their ascending sections, falling and horizontal must make up the effect, at which the right amount of heat will be received from the exhaust gas. The recommendation also contributes to this effect, to brake the exhaust gas outflow only to such an extent, at which the vacuum in the chimney is sufficient to pull the exhaust gas outwards. The foundation furnace heats mainly by emitting radiant heat.

The terms refer to the horizontal projection: 1 = combustion chamber and smoke ducts,
2 = furnace door, 3 = visible furnace wall, 4 = rear ventilation.