Abstract: A closed heating system for a building particularly adapted to be installed in a conventional fireplace for supplementing the heat generated by a conventional forced air heating unit. The heating system includes a grate having a log supporting water conduit through which water passes and is heated by the logs supported thereby. The heated water is pumped through suitable valves to a heat exchanger disposed within the air duct of a conventional forced air heating system to heat the air passing therethrough. The heated water may bypass the air duct heat exchanger. The bypassed water is communicated to a coil associated with a tempering tank which is installed in the building cold water supply line that feeds the hot water heater. The hot water preheats the water supply and is then returned to a storage tank for recycling.