Shenyang Third Thermal Heating Co., Ltd. is one of the largest companies of the central heating industry in Shenyang. The body and the middle partition wall of ZOZEN DHL series corner tube hot water boiler adopt membrane water wall complete sealing structure, which greatly reduces the boiler heat loss and improves the boiler thermal efficiency. Meanwhile, the flag heating surface of this series of boilers is designed with patented technology of the same smoke velocity in variable cross-section, so that the flow velocity of the smoke in heated surface between the high temperature zone and the low temperature zone is uniform, reducing the ash accumulation and increasing the heat transfer co-efficiency.