From a cold stove, full power (4kW) is achieved after 2.5 to 3 hours, but already after about 20 minutes you can feel the heat on the side of the stove.  By adding a total of 11 kg of wood in two to three rounds, the heat lasts over 24 hours, provided that the damper is pushed in when only live coals remain. Note that the damper must not be pushed fully in as long as there are blue flames that spread after stirring the live coals.