A dryer including ∘ a treating chamber where items are introduced and treated with a process air flow; ∘ a heat pump system having a refrigerant circuit in which a refrigerant can flow, said refrigerant circuit including a first heat exchanger where the refrigerant is heated up, a second heat exchanger where the refrigerant is cooled off, a compressor to pressurize and circulate the refrigerant through the refrigerant circuit, and a pressure-lowering device; said first and/or second heat exchanger being apt to perform heat exchange between said refrigerant flowing in said refrigerant circuit and said process air; the refrigerant being a flammable refrigerant; ∘ wherein said second heat exchanger: ▪ is a finned tube heat exchanger comprising a tube having multiple sections one above the other and a plurality of fins; ▪ is divided in three portions: a central portion wherein said multiple sections of the tube are in contact with said plurality of fins, and a first and second end portions (61, 62) where said tube is not in contact with the plurality of fins; ∘ characterized in that a ratio between a total external volume enclosed by the external surface of all sections of the tube included in the central portion in contact with the plurality of fins and a compressor displacement (Vmax) has a value higher than 35 and lower than 70 and wherein the length (Le) of the sections in said central portion is comprised between 200 mm and 300 mm. ∘ a treating chamber where items are introduced and treated with a process air flow; ∘ a heat pump system having a refrigerant circuit in which a refrigerant can flow, said refrigerant circuit including a first heat exchanger where the refrigerant is heated up, a second heat exchanger where the refrigerant is cooled off, a compressor to pressurize and circulate the refrigerant through the refrigerant circuit, and a pressure-lowering device; said first and/or second heat exchanger being apt to perform heat exchange between said refrigerant flowing in said refrigerant circuit and said process air; the refrigerant being a flammable refrigerant; ∘ wherein said second heat exchanger: ▪ is a finned tube heat exchanger comprising a tube having multiple sections one above the other and a plurality of fins; ▪ is divided in three portions: a central portion wherein said multiple sections of the tube are in contact with said plurality of fins, and a first and second end portions (61, 62) where said tube is not in contact with the plurality of fins; ▪ is a finned tube heat exchanger comprising a tube having multiple sections one above the other and a plurality of fins; ▪ is divided in three portions: a central portion wherein said multiple sections of the tube are in contact with said plurality of fins, and a first and second end portions (61, 62) where said tube is not in contact with the plurality of fins; ∘ characterized in that a ratio between a total external volume enclosed by the external surface of all sections of the tube included in the central portion in contact with the plurality of fins and a compressor displacement (Vmax) has a value higher than 35 and lower than 70 and wherein the length (Le) of the sections in said central portion is comprised between 200 mm and 300 mm.