Abstract: A system is provided for heating a building with solar energy by means of solar panels provided with hydronic sub-loops which connect with radiators separately heated by a furnace. Each hydronic sub-loop serves to supplement heat from the furnace and, while an integral part of each radiator, nevertheless is separate from the furnace system, and provides heat exchanging action therebetween. Separate circulating pumps, valves and control means are disclosed for operation in conjunction with a furnace and radiator circulating system.