In order to optimise the efficiency of tile stoves with a thermal capacity of up to 10 kW using wood logs, an important task is to investigate the heat storage of such firing systems used for space heating. For a basic understanding of heat transfer and heat storage behaviour, experiments as well as numerical simulations were carried out. Within the framework of these investigations, two different types of tile stoves were tested: a single-walled stove without an air gap and a double-walled stove with an air gap. Findings show that the air gap influences the heat storage behaviour causing a smooth surface temperature distribution and a decline in efficiency on the other hand. In order to avoid this negative effect, variations of the width of the air gap, ceramic mass, material and length of the flue gas tube were carried out. To remedy the deficiencies of the double-walled design, an extension of the length of the flue gas tube by 10-14% is necessary. Dense chamotte also allow double-walled tile stoves with the same efficiency as single-walled stoves using standard chamotte. (C) 2003 Published by Elsevier B.V.