A heat exchanger apparatus comprising: a heat exchanger, the heat exchanger having a primary side and a secondary side, the secondary side having connections for a secondary side inlet and a secondary side outlet, and the primary side having a connection for a primary side inlet (20; 19), wherein a first end of the heat exchanger has the connection for the primary side (20; 19) and one connection for the secondary side (18; 21), and wherein a second end of the heat exchanger has the other connection for the secondary side (21; 18); a primary circuit pump for propelling fluid through a primary circuit from the primary side inlet to a primary side outlet; a secondary circuit pump for propelling fluid through the secondary side of the heat exchanger and through a secondary circuit connected thereto from the secondary side inlet to the secondary side outlet; and a secondary side manifold arrangement (8, 6) for connecting the secondary pump to the heat exchanger and to the secondary circuit; wherein both the primary pump and the secondary pump are arranged in parallel with the line between the first end and the second end of the heat exchanger and each of the pumps have a pump inlet and pump outlet with inlet and outlet flow directions generally parallel to the line between the first end and the second end of the heat exchanger; characterised in that the primary side of the heat exchanger has a connection for the primary side outlet (19; 20), and the second end of the heat exchanger has the other connection (19; 20) for the primary side; in that the heat exchanger apparatus further comprises a primary side manifold arrangement (9, 12) for connecting the primary pump to the heat exchanger and to the primary circuit; in that the primary circuit pump is for propelling fluid through the primary side of the heat exchanger to which the primary circuit is connected; and in that the primary and secondary manifold arrangements each connect (9; 8) one connector (19; 20; 18; 21) of one side of the heat exchanger to an inlet or outlet of the respective primary or secondary pump, connect (12; 6) the second connector (20; 19; 21; 18) of said one side of the heat exchanger to the respective primary or secondary circuit (23; 22), and connect the respective primary or secondary circuit to the other of the inlet or outlet of the respective primary or secondary pump. a heat exchanger, the heat exchanger having a primary side and a secondary side, the secondary side having connections for a secondary side inlet and a secondary side outlet, and the primary side having a connection for a primary side inlet (20; 19), wherein a first end of the heat exchanger has the connection for the primary side (20; 19) and one connection for the secondary side (18; 21), and wherein a second end of the heat exchanger has the other connection for the secondary side (21; 18); a primary circuit pump for propelling fluid through a primary circuit from the primary side inlet to a primary side outlet; a secondary circuit pump for propelling fluid through the secondary side of the heat exchanger and through a secondary circuit connected thereto from the secondary side inlet to the secondary side outlet; and a secondary side manifold arrangement (8, 6) for connecting the secondary pump to the heat exchanger and to the secondary circuit; wherein both the primary pump and the secondary pump are arranged in parallel with the line between the first end and the second end of the heat exchanger and each of the pumps have a pump inlet and pump outlet with inlet and outlet flow directions generally parallel to the line between the first end and the second end of the heat exchanger; characterised in that the primary side of the heat exchanger has a connection for the primary side outlet (19; 20), and the second end of the heat exchanger has the other connection (19; 20) for the primary side; in that the heat exchanger apparatus further comprises a primary side manifold arrangement (9, 12) for connecting the primary pump to the heat exchanger and to the primary circuit; in that the primary circuit pump is for propelling fluid through the primary side of the heat exchanger to which the primary circuit is connected; and in that the primary and secondary manifold arrangements each connect (9; 8) one connector (19; 20; 18; 21) of one side of the heat exchanger to an inlet or outlet of the respective primary or secondary pump, connect (12; 6) the second connector (20; 19; 21; 18) of said one side of the heat exchanger to the respective primary or secondary circuit (23; 22), and connect the respective primary or secondary circuit to the other of the inlet or outlet of the respective primary or secondary pump.