There are two basic types of active solar heating systems based on the type of fluid—either liquid or air—that is heated in the solar energy collectors. The collector is the device in which a fluid is heated by the sun. Liquid-based systems heat water or an antifreeze solution in a "hydronic" collector, whereas air-based systems heat air in an "air collector."
Both of these systems collect and absorb solar radiation, then transfer the solar heat directly to the interior space or to a storage system, from which the heat is distributed. If the system cannot provide adequate space heating, an auxiliary or back-up system provides the additional heat. Liquid systems are more often used when storage is included, and are well suited for radiant heating systems, boilers with hot water radiators, and even absorption heat pumps and coolers. Both air and liquid systems can supplement forced air systems.
Visit the Energy Saver website for more information about active solar heating in homes, including the economics, selection and sizing, control systems, building codes and covenants, and installation and maintenance.