A submerged combustion heat-generator enabling the obtention of a high-temperature heat-carrying fluid. The heat generator of the invention uses a burner operating on combustion in a liquid bath, for instance of water and the combustion gases burn in a combustion chamber which is at least partially immerged in the said bath and at least partially heat-insulated therefrom. Said combustion chamber comprises a second heat-exchanger which is mounted upstream of said first exchanger on the heat-carrying fluid path.