During the winter, your desired comfort level is set at 72o in your thermostat. Suddenly, the temperature in your home drops to 71o. Immediately, the thermostat sends a signal to the furnace. The furnace ignites the pilot light to heat the main burner. Heat is then drawn from the burner and is forced by a blower fan through the ductwork to warm the house. As the warm air blows through the vents, the cooler air is pulled through the intake back to the furnace to be heated. Finally, the temperature in your home has reached 72o. The thermostat sends another signal to the furnace. The furnace shuts off all the heating elements and distributes any remaining heated air before shutting off the fan.