Outdoor swimming pools are becoming commonly exploited even in wintertime as they represent a good attraction in the hotel industry to compete with geothermal pools available only in some countries. The present study proposes a numerical model for outdoor swimming pools based on the energy balance methodology. Conduction to the ground, convection and evaporation at the pool’s surface are taken into account in the formulation among with other heat loss sources and gains. The model is validated with experimental data from a pool exploited in a real hotel. The simulation shows that by adequately operating the pool with optimizing pool-cover time and backwash ratio, energy savings in exploitation can be achieved. Some modifications on the pool design are proposed to reduce energy consumption.