Abstract: A method and apparatus for utilizing the earth or other heat source/heat sink for heating and cooling buildings are disclosed. The system comprises at least one heat transfer fluid conduit and at least one heat pipe in heat transfer communication. When two conduits are employed a dual cycle system for heating and cooling is disclosed. In the preferred embodiment, upper and lower heat transfer fluid conduits containing a first heat transfer fluid are connected by heat pipes containing a second heat transfer fluid, the two fluids being isolated from one another. The heat pipes are preferably sealed plastic tubes with hollow metal end caps at each end. The metal end caps on the heat pipes are positioned in the circulation pipes so as to have sufficient contact with the recirculatory fluid in the respective heat transfer fluid conduits to transfer heat to and from such fluid.