An Excel macro-programming model of the thermal behaviour of open and enclosed swimming pools is run in seven different scenarios of increasing complexity. To secure a swimming season for the whole year, the use of a tent, a battery of collectors and auxiliary heat, to cope with winter, is advice. The tent can be removed or vented from November to March and must be tightly closed the rest of the year. An area of collectors equal to half the pool area will avoid excessive overheat and will assure the use of the pool in the morning during summer. The calculated yearly solar participation in energy consumption is 43% for a water temperature greater than 26ºC.