What is the difference between single stage and two stage efficiency furnaces?

Single stage furnace is a basic furnace. When the thermostat calls for heat, the furnace starts up at maximum capacity and runs until the heat call is satisfied. A two stage furnace works differently and will save you money in the spring, summer and fall, when you don’t require as much heat. When the thermostat calls for heat, the two stage furnace starts up at about 65% of the furnaces capacity and the fan speed is lower. If the heat call is not satisfied within ten minutes, the furnace will increase the gas pressure and fan speed to full capacity to satisfy the call for heat.