According to the International Energy Agency, buildings are the largest energy-consuming sector globally, producing over one-third of greenhouse gas emissions in 2013. Renewable energies such as solar can be harnessed to fully or partially meet the energy demands of buildings. In this study, solar thermal collectors are used in a building to provide the hot water required for an underfloor heating system. Three cities in Iran, namely Tabriz, Tehran and Kish island, with distinctive climatic conditions are considered to gain a better understanding of the performance of solar-powered underfloor heating systems in different climates. Moreover, an economic analysis is conducted to assess the feasibility of the proposed system. DesignBuilder software is applied to simulate the energy performance of the building. The results indicate that the annual fuel consumption of the building with a solar collector located in Tehran, Tabriz and Kish island is reduced by 125.39, 303.58 and 1.41 MWh compared to that of without collector, respectively. The payback period of the system for Tehran, Tabriz and Kish Island is found to be 8.2, 9.4 and 12.1 years, respectively. (C) 2018 Elsevier Ltd. All rights reserved.