A steam generator or water heater that uses energy such as geothermal or solar energy.

Class A boiler:rated working pressure (gauge pressure, the same below) P ≥ 3.8 MPa boiler, including: 1. Ultra-supercritical boiler: P ≥ 27.0MPa or rated outlet temperature ≥ 590 ° C boiler; 2. Supercritical boiler: 22.1MPa≤P<27.0MPa; 3. Subcritical boiler: 16.7MPa≤P<22.1MPa; 4.UHP boiler: 13.7MPa≤P<16.7MPa; 5.High pressure boiler: 9.8MPa≤P<13.7MPa;6 Sub-high pressure boiler: 5.4MPa ≤ P < 9.8MPa; 7. Medium pressure boiler: 3.8MPa ≤ P < 5.4MPa.

Class B boiler:1. Steam boiler: 0.8MPa1.0t/h; 2. Hot water boiler: rated outlet temperature ≥120°C or rated thermal power>4.2MW; 3. Organic heat Carrier boiler: (1) boiler using gas phase organic heat carrier; (2) liquid phase organic heat carrier boiler: rated thermal power > 4.2 MW.

Class C boiler, the following boilers except D-class boiler:1. Steam boiler: steam boiler with rated working pressure ≤0.8MPa and rated evaporation ≤1.0t/h; 2.Hot water boiler: rated effluent temperature <120°C and Rated thermal power ≤ 4.2MW; 3. Liquid phase organic heat carrier boiler: rated thermal power ≤ 4.2MW.

Class D boiler:1. Steam boiler: water volume ≤ 50L and rated working pressure <0.8MPa when designing normal water level; 2. Steam-water dual-purpose boiler: boiler with rated working pressure ≤0.04MPa and rated evaporation ≤0.5t/h; E Only hot water boiler pressurized with tap water, and the water temperature is ≤ 95 °C.