Heat exchanger design for low energy buildings with thermal block energy storage is a critical component of the overall system performance. Geometric modifications proposed to improve the effectiveness of a heat exchanger in such a building have been examined through simulations and experiments. Of the considered modifications, one configuration (inserting chimney-sweep brushes) was only considered experimentally due to the difficulty of Meshing such a complex geometry. Other configurations were considered numerically as possible future modifications. Comparison of the resulting experimental and numerical results indicate that a 30% increase in heat exchanger effectiveness is achieved through use of the brushes, which exceeds the improvements predicted for the other configurations. These results indicate that no further modification of the heat exchanger is needed. (C) 2016 Elsevier B.V. All rights reserved.