There are several choices available for heating your home. The most common used heating sources is the furnace and boiler systems. Furnaces heat air and travel through ducts which is distributed into the home. While boilers heat water and is distributed to pipes and then to the radiators. High-efficiency heating systems are also available. There are several systems of furnaces and boilers; forced-air systems, hot-water systems, and steam systems. It depends on existing fixtures to which type of furnace or boiler system is used.