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 metallic pipe, wherein said flammable refrigerant flows, bent to define a coil structure comprising a plurality of straight sections, parallel one another and connected in twos at one end thereof by a plurality of curved sections, wherein the external diameter (de) of said metallic pipe is comprised between 5 and 9 mm; - a plurality of fins, stacked, spaced and parallel to one another, each provided with a plurality of through-holes, each through-hole housing two of said straight sections, said plurality of straight sections being distributed in such a way that, in a cross section whose cutting plane (Cp) is perpendicular to said straight sections, their centers (Ce) are aligned along a plurality of mutually parallel straight lines, characterized in that - the distance (Tp) between the centers (Ce) of two adjoining straight sections aligned along a same straight line among said mutually parallel straight lines is comprised between 30 and 40 mm, and the distance (Rp) between two adjoining straight lines among said mutually parallel straight lines is comprised between 12 and 50 mm, or - the distance (Tp) between the centers (Ce) of two adjoining straight sections aligned along a same straight line among said mutually parallel straight lines is comprised between 40 and 70 mm, and the distance (Rp) between two adjoining straight lines among said mutually parallel straight lines is comprised between 8 and 50 mm. - 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 metallic pipe, wherein said flammable refrigerant flows, bent to define a coil structure comprising a plurality of straight sections, parallel one another and connected in twos at one end thereof by a plurality of curved sections, wherein the external diameter (de) of said metallic pipe is comprised between 5 and 9 mm; - a plurality of fins, stacked, spaced and parallel to one another, each provided with a plurality of through-holes, each through-hole housing two of said straight sections, - a metallic pipe, wherein said flammable refrigerant flows, bent to define a coil structure comprising a plurality of straight sections, parallel one another and connected in twos at one end thereof by a plurality of curved sections, wherein the external diameter (de) of said metallic pipe is comprised between 5 and 9 mm; - a plurality of fins, stacked, spaced and parallel to one another, each provided with a plurality of through-holes, each through-hole housing two of said straight sections, said plurality of straight sections being distributed in such a way that, in a cross section whose cutting plane (Cp) is perpendicular to said straight sections, their centers (Ce) are aligned along a plurality of mutually parallel straight lines, characterized in that - the distance (Tp) between the centers (Ce) of two adjoining straight sections aligned along a same straight line among said mutually parallel straight lines is comprised between 30 and 40 mm, and the distance (Rp) between two adjoining straight lines among said mutually parallel straight lines is comprised between 12 and 50 mm, or - the distance (Tp) between the centers (Ce) of two adjoining straight sections aligned along a same straight line among said mutually parallel straight lines is comprised between 40 and 70 mm, and the distance (Rp) between two adjoining straight lines among said mutually parallel straight lines is comprised between 8 and 50 mm. - the distance (Tp) between the centers (Ce) of two adjoining straight sections aligned along a same straight line among said mutually parallel straight lines is comprised between 30 and 40 mm, and the distance (Rp) between two adjoining straight lines among said mutually parallel straight lines is comprised between 12 and 50 mm, or - the distance (Tp) between the centers (Ce) of two adjoining straight sections aligned along a same straight line among said mutually parallel straight lines is comprised between 40 and 70 mm, and the distance (Rp) between two adjoining straight lines among said mutually parallel straight lines is comprised between 8 and 50 mm.