Condensing boiler

A condensing boiler comprising an outer enclosure defining internally a chamber for containing water to be heated, which is provided with an inlet which can be connected to a duct for the return of cold water and with an outlet which can be connected to a duct for the delivery of hot water, and accommodating internally a combustion chamber, which is associated with a burner and is connected to a plurality of heat exchange tubes which pass through said containment chamber and lead, with an outlet end thereof, into a fume collection chamber, which is substantially cylindrical and is connected to a fume evacuation stack, inside said fume collection chamber there being a condensing device for the fumes that arrive in said fume collection chamber, wherein said stack has an intake which is arranged substantially coaxially to said fume collection chamber and in that said condensing device comprises at least one fume cooling element which has a substantially annular shape and is arranged substantially coaxially to said fume collection chamber in order to be skimmed radially on its outer surface by a flow of the fumes that arrive from said heat exchange tubes and are directed toward the intake of said stack.