Abstract: A solar heating system for use in combination with a forced draft heating system for heating ventilation air of a building. The solar heating system includes a solar collector assembly for heating a liquid circulated through the assembly. The heated liquid is stored in an insulated storage tank where it can be circulated through a heat exchanger positioned in an air duct of the forced draft heating system as need to heat air flow through the duct. The use of a liquid as the heat transfer fluid and providing a storage facility for heated liquid permits the heating system to operate for a period of time after the sun sets or becomes ineffective in providing solar radiation until the heat stored in the liquid becomes exhausted. To increase the heat storage capacity of the liquid, one or more heat sinks can be utilized to absorb excess heat from the liquid and then transfer the absorbed heat back to the liquid when an opposite thermal gradient exists.