There are two types of active solar heating systems: an air circulation system and a liquid circulation system.
Air-circulation systems are mounted on a roof or south-facing wall of a room. A large, flat panel that's darkened and non-reflective is used as a solar collector. A protective, transparent cover is placed over top the darkened surface to create a narrow air-chamber. As the panel absorbs the solar radiation, it heats the air in the chamber. A simple fan then circulates the heated air from the top of the unit while bringing in cooler air at the bottom. The fan helps to speed the natural convection flow of the air and helps keeps the room at a comfortable temperature.
These systems are effective for heating rooms or open floor plans. Only indoor air should be circulated in the system since outside air may be too cold to be sufficiently warmed by the collector.
These systems also use a large, flat solar collector. Tubes filled with an ethylene glycol (anti-freeze) solution snake back and forth behind the panel to absorb the solar heat. The heated liquid is then stored in an insulated tank which can then be used to heat the home. Water should not be used as a heat-transfer medium since it may freeze in winter.
These solar power systems work well with in-floor radiant heating systems which already have installed plumbing. Heat exchanges can also be installed to transfer the heat from the ethylene glycol to a household hot water system.
Both types of active solar heating systems are excellent supplementary energy systems for homes, and can help save on residential heating costs.