The "Euromonitor" gas steam boiler series launched by Fangkuai adopts a closed condensate water recovery system to directly send high-temperature condensate water into the boiler for reuse. Combined with a three return structure, energy-saving device, and air preheater, it fully utilizes the heat of flue gas, combining sensible heat and latent heat in the flue gas heat to recover and utilize the heat of high-temperature condensate water from the source. This not only saves fuel costs and operating expenses, but also improves the overall operating efficiency of the boiler, achieving a win-win situation.