This series are boilers for heating and hot water, with double-pipe heat exchanger and adopt the Denmark Grundfos G20 water pump, which runs quietly and the circulation performance is excellent. This product has obtained the national patent with the patent certificate number of ZL201220319328.6 and ZL201530085084.9. With high thermal efficiency, the boiler reaches the national secondary energy efficiency standard. The fuel gas proportional type automatically adjusts the output size of fuel gas flow, and the hot water temperature maintains a constant temperature to meet the domestic hot water needs of customers.