A laundry treating appliance comprising: - a cabinet; - a drum, rotatably housed within said cabinet, in which laundry can be loaded; - a heat pump system, using one or more flammable refrigerants, configured for exchanging heat with an operating fluid; - a circulating system configured for circulating said operating fluid through said drum; wherein said heat pump system comprises a heat exchanger (70a, 70b) comprising: - a plurality of metallic pipes wherein said flammable refrigerant flows; - a plurality of fins, stacked, spaced and parallel to one another, each provided with four or more substantially circular through-holes suitable for housing one of said metallic pipes and having a closed perimeter, wherein said straight pipes are radially expanded so as to fit with their lateral surface into close contact with the border of said respective through-hole, in such a way to obtain an effective heat-exchange between them, wherein each of at least two through-holes of said four or more through-holes of each one of said fins houses one of said metallic pipes, wherein said metallic pipes comprise two or more straight pipes, parallel one another and perpendicular to said fins, each one of said two or more straight pipes being housed in one of said four or more through-holes of said fins, said two or more straight pipes being connected in twos, at one end, by a curved pipe, to define as a whole a single duct wherein said flammable refrigerant flows, characterized in that at least two through-holes of said four or more through-holes of each one of said fins do not house any of said metallic pipes. - a cabinet; - a drum, rotatably housed within said cabinet, in which laundry can be loaded; - a heat pump system, using one or more flammable refrigerants, configured for exchanging heat with an operating fluid; - a circulating system configured for circulating said operating fluid through said drum; wherein said heat pump system comprises a heat exchanger (70a, 70b) comprising: - a plurality of metallic pipes wherein said flammable refrigerant flows; - a plurality of fins, stacked, spaced and parallel to one another, each provided with four or more substantially circular through-holes suitable for housing one of said metallic pipes and having a closed perimeter, - a plurality of metallic pipes wherein said flammable refrigerant flows; - a plurality of fins, stacked, spaced and parallel to one another, each provided with four or more substantially circular through-holes suitable for housing one of said metallic pipes and having a closed perimeter, wherein said straight pipes are radially expanded so as to fit with their lateral surface into close contact with the border of said respective through-hole, in such a way to obtain an effective heat-exchange between them, wherein each of at least two through-holes of said four or more through-holes of each one of said fins houses one of said metallic pipes, wherein said metallic pipes comprise two or more straight pipes, parallel one another and perpendicular to said fins, each one of said two or more straight pipes being housed in one of said four or more through-holes of said fins, said two or more straight pipes being connected in twos, at one end, by a curved pipe, to define as a whole a single duct wherein said flammable refrigerant flows, characterized in that at least two through-holes of said four or more through-holes of each one of said fins do not house any of said metallic pipes.