In this paper, we analyse the thermal behaviour and the environmental impact of an indoor swimming pool placed in Pozo Estrecho, Cartagena, in the Southeast of Spain. The existing installation is formed by a group of solar thermal collectors supported by two propane heaters which heat the water of the pool and satisfy the needs of hot water in the changing room of the pool. Here we propose an installation based on the use of a heat pump supported by solar thermal collectors. In this work, we first describe the installations. They are modelled with Trnsys and the models employed briefly described. Later, we compare their primary energy consumption and its environmental impact in terms of their CO2 emissions. A rough estimate of its economic impact is also given. Some conclusions are finally drawn.