Abstract: A radiator for use in hot water central heating systems is constructed from extruded aluminium alloy sections. One finned configuration of section having a tubular duct extending therethrough is used as the heat exchanger which interconnects the fluid flow and return headers. These each incorporate locking flanges which interlock with respective external slots pre-formed in the fins on each side of the heat-exchanger sections. Pressure tight fluid connections between the headers and the duct in each heat-exchanger section are made by double-ended chamfered barrel nipples.