A heat exchanger for absorbing heat from a medium across a substantially planar surface, the exchanger comprising: a heat exchanging panel; a fluid circuit comprising a first chamber disposed at a first end of the panel, a second chamber disposed at a second end of the panel, a plurality of passages which extend along the panel between the first and second chambers (104, 105), and a duct which extends between the first and second chamber (104, 105); a fluid disposed within the circuit; wherein, the plurality of passages are arranged in thermal communication with the panel and are arranged to communicate the fluid from the first chamber to the second chamber, and the duct is arranged to communicate fluid from the second chamber to the first chamber, and wherein the panel comprises a heat exchanging surface which is arranged to extend adjacent the medium, wherein the first chamber is arranged to extend at a vertical height which is below the second chamber, such that the fluid can pass from the second chamber to the first chamber along the duct, under the influence of gravity, and wherein the second chamber comprises a cooler for cooling the fluid disposed within the chamber, the cooler comprising a cooling duct which is arranged to extend within the chamber for communicating a cooling fluid between an inlet and an outlet of the cooling duct, characterised in that the first and second chambers (104, 105) are arranged to extend away from the panel from the side opposite the heat exchanging surface, and in that also the first chamber comprises a cooler for cooling the fluid disposed within the chamber, the cooler comprising a cooling duct which is arranged to extend within the chamber for communicating a cooling fluid between an inlet and an outlet of the cooling duct, and wherein the outlet of one cooling duct is coupled to the inlet of the other cooling duct. a heat exchanging panel; a fluid circuit comprising a first chamber disposed at a first end of the panel, a second chamber disposed at a second end of the panel, a plurality of passages which extend along the panel between the first and second chambers (104, 105), and a duct which extends between the first and second chamber (104, 105); a fluid disposed within the circuit; wherein, the plurality of passages are arranged in thermal communication with the panel and are arranged to communicate the fluid from the first chamber to the second chamber, and the duct is arranged to communicate fluid from the second chamber to the first chamber, and wherein the panel comprises a heat exchanging surface which is arranged to extend adjacent the medium, wherein the first chamber is arranged to extend at a vertical height which is below the second chamber, such that the fluid can pass from the second chamber to the first chamber along the duct, under the influence of gravity, and wherein the second chamber comprises a cooler for cooling the fluid disposed within the chamber, the cooler comprising a cooling duct which is arranged to extend within the chamber for communicating a cooling fluid between an inlet and an outlet of the cooling duct, characterised in that the first and second chambers (104, 105) are arranged to extend away from the panel from the side opposite the heat exchanging surface, and in that also the first chamber comprises a cooler for cooling the fluid disposed within the chamber, the cooler comprising a cooling duct which is arranged to extend within the chamber for communicating a cooling fluid between an inlet and an outlet of the cooling duct, and wherein the outlet of one cooling duct is coupled to the inlet of the other cooling duct.