This depends on when you’re using the heater. In the summer, you likely won’t need the heater running during the day because the temperature outside will keep it warm. At night, it could become cooler, so you may want to turn the heater on before you go to bed to ensure the pool is warm in the morning. During the spring and fall, when the days and nights are both cool, you may need to keep the heater running at all times to maintain the warmer water temperature.