A heat exchanger (1) has an exchanger unit (20), comprising at least one first coiled conduit and one second coiled conduit (21, 23) that are substantially coaxial, and a casing (2) for housing the exchanger unit (20). The casing (2) has a first end wall (3), a second end wall (4), and a peripheral part (5) between the two end walls (3, 4). Each conduit (21 -23) has an inlet and an outlet, where the outlet of the first conduit (21, 23) is connected substantially in series to the inlet of the second conduit (22). The exchanger unit (20) is supported by the first end wall (3) of the casing (2), with the inlet of the first conduit (21) and the outlet of the second conduit (22) which are substantially at the first end wall (3) of the casing (2)·