An apparatus for heating an operating fluid, the apparatus comprising a closed circuit for a working fluid, the closed circuit having first and second heat exchangers and a compressor therebetween, the first heat exchanger having a heat input side for connection to an external fluid heat source and a heat output side for vaporizing working fluid within the closed circuit, the compressor being a vapor compressor adapted to compress the vaporized gaseous working fluid from the first heat exchanger to form a higher pressure gaseous working fluid, and the second heat exchanger having a heat input side for receiving and condensing the higher pressure gaseous working fluid from the compressor and a heat output side for heating an external operating fluid. A corresponding method is also disclosed.