The present invention relates to a boiler system using waste heat, capable of reasonably using fuel. According to the present invention, the boiler system using waste heat comprises: a boiler to heat circulation water; a circulation water supply unit; a fuel supply unit to supply fuel for heating the circulation water to the boiler; and an air pre-heater sucking air from the outside and using exhaust gas generated in accordance with combustion of the fuel to heat the suck air and supply the heated air to the boiler.
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