The integrated horizontal condensing atmospheric hot water boiler adopts counterflow heat transfer, step-by-step cooling method, and large furnace radiation heat transfer; Turbulent convection heat transfer in the smoke duct area; And ultimately condense the tail flue gas, allowing the sensible and latent heat of the fuel to be fully absorbed. Fully intelligent control, once put into operation, the boiler automatically runs, with automatic adjustment of water level, water temperature, etc. It has complete functions and a flue gas monitoring device that can automatically monitor the exhaust temperature of the boiler, making it more convenient to grasp the combustion situation of the boiler.