It can be formed into a large coil combustion chamber, which can achieve low temperature combustion, greatly reduce nitrogen oxide emissions, and clean smoke exhaust under the premise of higher vertical thermal efficiency. The horizontal type can make the boiler into high power, and the high-density ring tube design structure makes the boiler power volume ratio small, saving space for customers. The flow section structure of multi-return heat transfer is reasonable, the flow load is uniform and the operation is stable. The system has stable control, easy operation and safe operation. The spiral coil inside and outside the furnace body is composed of multiple small pipe diameters, which has good thermal expansion performance and low pressure. Good temperature, pressure and smoke temperature protection control.