Solar Insolation Map Use the map and chart below to determine the potential extended swimming season for your area Swimming Seasons Zone No Heater Solar Heater Heat Pump 1 6-7 months 12 months 12 months 2 4-5.5 months 10-11 months 12 months 3 4.5 months 9 months 10 months 4 3-4 months 8 months 9 months 5 3 months 6 months 6.5 months 6 2 months 4 months 5 months 7 1-1.5 months 3 months 3-4 months An electric heat pump extends your swimming season slightly longer, but a solar pool heater has NO operating costs. Learn all about Solar Pool Heaters View Solar Pool Heater Installations September's Special: FREE POOL COVER!