A heating boiler comprising a water inlet manifold (2), water outlet manifold (1) and a plurality of extruded aluminium finned tubes (3) extending between the manifolds (1 and 2) and communicating therewith in a watertight manner by way of press-fit ferrules (10). Two rows of tubes (3) are arranged within the casing (18) against opposite side walls and enclose a cavity which is split by a platform (21) into a combustion chamber (6) having a burner (11) and an exhaust chamber (23) having a flue (15). Combustion products pass from the combustion chamber into an intermediate zone (7) and thence into a condensation zone (8) where baffle (16) directs the products of combustion onto the fins of the tubes (3). In this latter zone condensation occurring on the fins is collected in tray (24) and may be drained via a port (25).