 is programmed to come on with the furnace and the furnace only kicks on in extreme conditions so it's all computerized so you can set it when the furnace comes on and when the heat pump is used less and and so in other words if it gets really extreme where the heat pump wouldn't handle it that the furnace comes on but the furnace doesn't have to work as hard because it has the heat pump and then the heat pump of course is being paid for by solar