Seasonal energy storage can be achieved by hot water injection in geothermal sandstone aquifers. We present an analysis of literature data in combination with new short-term flow through permeability experiments in order to address physical and physico-chemical mechanisms that can alter permeability when sandstones are heated from 20 degrees C to 70-200 degrees C. The pore surface area per unit pore volume was used to normalise permeability data, so that the temperature effect on samples with different pore size could be compared. In sandstones containing the clay mineral kaolinite, heating reduced permeability, suggesting that the observed permeability reduction was due to kaolinite mobilisation. The effect was partly reversible. (C) 2013 Elsevier Ltd. All rights reserved.