Solar sunrooms are a form of passive solar heating. But the sun can heat more than just the sunroom itself, you can use the sunroom to distribute the free heat collected throughout your home. Solar sunrooms are a type of isolated solar gain system.
In such a system heat is collected remote from the main structure of the house, i.e. the sunroom, and then distributed, via convection through vents into the living space or conduction through a shared, thermal wall. For rooms that are completely isolated from the main living space, a convective loop through an air collector is used to move the warm air to a storage system in the main house.
Some sunrooms are designed with thermostats to activate mechanical fans when the room exceeds a set temperature. However, it should be noted that use of mechanical fans to distribute warm air results in an active, not passive, system. The thermal walls attaching the sunroom to the house are usually constructed from conductive materials such as brick, concrete, adobe/earth materials, and may even utilize water.
Solar sunrooms are most effective when south-facing. Windows are coated with a low-E glazing, although overhead glazing is unnecessary, to maximize heat gain. In hot areas it may even be a good idea to use a heat-reflective glazing overhead to prevent overheating. In such cases it is also important to ventilate the sunroom itself when necessary. Solar sunrooms also have the advantage of adding usable space to the home and can act as a greenhouse for growing plants.