Like heat pumps, furnaces keep your home warm in the winter and serve as an important part of your air conditioning system in the summer. In a furnace, gas or oil is combusted in a burner and then heat produced from that reaction passes through a heat exchanger where it is transferred to the air distribution system. The ductwork throughout a home carries and disperses the conditioned air and the flue or vent pipe releases the byproducts, such as carbon dioxide and water vapor, outside the home.