Introduction: The low NOx gas boiler is the gas-fired boiler which can significantly reduce the emission of nitrogen oxide (NOx) via emerging and advanced technologies. In addition, harmful substances such as CO2, SOx and particulates are also greatly reduced at the same time. ZOZEN's WNS and SZS series gas-fired steam boiler introduces the low NOx burner to meet the strict environmental protection standard of low NOx emission. The third-party EIA test shows that the flue gas NOx content is 14-17mg/m3, which is far lower than the environmental protection standard of 30mg/m3. In general, the low NOx gas boiler is highly-efficient, energy-saving and eco-friendly.