Abstract: A heliothermal heating and cooling system of the type using a heat transport fluid such as water is disclosed. The energy collector comprises an assembly of individual solar collector panel modules in a series/parallel configuration and function to heat water flowing therethrough. Each solar collector panel includes a pair of stepped headers respectively disposed at its input and output portions and which function to reduce water flow resistance therethrough. The input and output headers communicate with an insulated water storage tank by way of return and supply lines, respectively. A pump is provided in the return line to circulate the water through the system upon receipt of a command signal. The storage tank communicates with a thermal energy utilization device and includes an integral, internal expansion chamber to accomodate expansion of the water.