Abstract: The thermal efficiency of boiler depends on heat loss of exhaust gas in a large extent. Lowering the temperature of exhaust gas below dew point of water not only can its sensible heat of uncondensible gases be decreased, but also the steam evaporation latent heat can be recovered by oil-fired and gas-fired conden- sation boilers, so the heat loss of exhaust gas will be decreased and the thermal efficiency of boiler will be improved in quantities. Oil-fired and gas-fired condensation boilers are economic, water saving and low pol- lution. This paper analyzes the energy saving efficiency of the boiler.