A device for generating hot air by means of biomass combustion which comprises an auger feeder, a receiving hopper, a combustion chamber with a burner, the combustion chamber comprising recesses, a heat-exchanger unit between two gaseous fluids: a first fluid and a second fluid, the heat-exchanger unit comprising upper and lower caissons, with recesses; a blower fan of the second gaseous fluid, a first outlet of the first gaseous fluid and a second outlet for the second gaseous fluid; wherein: - the first gaseous fluid is a stream of hot gases generated by the combustion of biomass within the combustion chamber, while the second gaseous fluid is a flow of hot air expelled from the second outlet; - the heat-exchanger unit comprises several groups of second vertical tubes, whose ends lead into recesses of the upper caissons and of the lower caissons; wherein the first gaseous fluid flows inside second vertical tubes and upper and lower caissons,, following a sinusoidal path formed by updrafts and downdrafts corresponding to the second vertical tubes, and by other currents flowing through the inside of the upper and lower caissons,; and - the first and second vertical tubes, are housed inside a main chamber of the heat-exchanger unit which communicates with a casing chamber located around a structure of the combustion chamber; wherein the stream of the second gaseous fluid of air first flows through the main chamber receiving heat from the first and second vertical tubes, and then flows through the casing chamber wherein the second gaseous fluid of air increases its temperature through the heat transferred by the combustion chamber; ending up in the casing chamber in the second outlet for hot air, the device being characterized in that: - the heat-exchanger unit comprises an independent structure which is detachably coupled to the structure of the combustion chamber; wherein the flow of the first gaseous fluid from the combustion chamber to the heat-exchanger unit comprises first vertical tubes which are detachable, which have lower end sections which fit into recesses of the combustion chamber, and upper end sections which fit into recesses of a first upper caisson of the heat-exchanger unit; wherein the first gaseous fluid ascends from a lower portion of the combustion chamber to the first upper caisson of the heat-exchanger unit through the first vertical tubes. - the first gaseous fluid is a stream of hot gases generated by the combustion of biomass within the combustion chamber, while the second gaseous fluid is a flow of hot air expelled from the second outlet; - the heat-exchanger unit comprises several groups of second vertical tubes, whose ends lead into recesses of the upper caissons and of the lower caissons; wherein the first gaseous fluid flows inside second vertical tubes and upper and lower caissons,, following a sinusoidal path formed by updrafts and downdrafts corresponding to the second vertical tubes, and by other currents flowing through the inside of the upper and lower caissons,; and - the first and second vertical tubes, are housed inside a main chamber of the heat-exchanger unit which communicates with a casing chamber located around a structure of the combustion chamber; wherein the stream of the second gaseous fluid of air first flows through the main chamber receiving heat from the first and second vertical tubes, and then flows through the casing chamber wherein the second gaseous fluid of air increases its temperature through the heat transferred by the combustion chamber; ending up in the casing chamber in the second outlet for hot air, - the heat-exchanger unit comprises an independent structure which is detachably coupled to the structure of the combustion chamber; wherein the flow of the first gaseous fluid from the combustion chamber to the heat-exchanger unit comprises first vertical tubes which are detachable, which have lower end sections which fit into recesses of the combustion chamber, and upper end sections which fit into recesses of a first upper caisson of the heat-exchanger unit; wherein the first gaseous fluid ascends from a lower portion of the combustion chamber to the first upper caisson of the heat-exchanger unit through the first vertical tubes.