The split horizontal atmospheric hot water boiler is a shell type fully wet back center reigning hot pot structure. The furnace chamber adopts a large volume to ensure uniform airflow inside the chamber. The fuel is atomized by the burner and burned under slight positive pressure inside the furnace chamber. The high-temperature flue gas flows backwards along the furnace chamber to the bottom of the furnace at a 180 degree angle and undergoes radiative heat transfer inside the furnace chamber in the atmosphere. Fully automatic control, equipped with original imported burners, computer simulation control design throughout the process, optimized design of heating surface and flue gas flow, more compact structure, and easier installation and maintenance.