Solar Heaters utilize the sun's free heat and do not have an operating cost. Your existing pool pump circulates the water through the heater, usually located on the roof, and warms the pool. The pump timer is set to operate during sunlight hours, usually 9am to 5pm. An Automatic Control and Valve are sometimes used to regulate temperature, usually in northern climates or where absolute temperature control is desired. Commercial pools and some larger residential pools may need a booster pump.