A condensation exchanger for heating of water and for production of sanitary water, providing a first inner coil with plain surface, and a second outer coil, said second coil being externally spirally wound with respect to said first coil, within said coils circulating a thermal carrier fluid, said first coil exchanging heat with combustion fumes by radiation and convection, and said second coil exchanging heat with the combustion fumes by condensation, wherein said second coil has a plain surface, and in that an insulating septum is provided, said septum dividing said exchanger in a first upper or combustion zone, and a second lower zone, said insulating septum dividing said exchanger in said two areas with a ratio of: 45%≤H1L≤60%.