Flooded former coal mines of Springhill, Nova Scotia, contain about 4,000,000 m3 of water which circulates by convection and may be recovered at the surface at a temperature of about 18-degrees-C. The heat in the water is derived from the normal heat of the rocks, and the contribution from chemical heating is negligible. Water is pumped from the mines to act as the primary input to heat pumps for heating and cooling industrial buildings. Annual heat exchange with the mine by the largest user puts more heat into the mine in summer than is taken out in winter. Buildings without heavy machinery, such as office buildings, drain little heat from the mine, so that many heat exchange systems could operate indefinitely, without significant depletion of the heat source. Initial costs of heat pump installation are higher than the costs of conventional oil furnaces, but the operating costs are substantially lower. In the Springhill systems, heat pumps provide summer cooling as well as winter heating, and total costs of geothermal heating are substantially lower than heating by fuel oil in eastern Canada. There is a net saving in the emission of carbon dioxide to the atmosphere.