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 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 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 . <EOS>