Abstract: The invention relates to a method of recovering thermal energy from sea water and comparable water masses. Sea water is supplied in a constant or variable flow to a heat exchanger (3) and returned to the sea. A heat carrying medium is pumped simultaneously through the heat exchanger (3) and a supply conduit (7,11) to an evaporator for a per se known heat pump (8) and through a return conduit (12,9) again to the heat exchanger (3). The medium is pumped in a flow exceeding the flow through the evaporator, and a part of the medium is directed from the supply conduit (7) past (10) the evaporator and to the return conduit (9). The sea water flow is of a size at least equal to the medium flow.