Fuels used in hot water boilers can be mainly divided into four categories:
(1) Solid fuels - bituminous coal, anthracite, lignite, peat, oil shale, wood chips, bagasse, rice bran, etc.
(2) Liquid fuel - heavy oil, residual oil, diesel oil, etc.
(3) Gas fuel - natural gas, city gas, liquefied petroleum gas, etc.
(4) New fuels—electric energy, light energy, etc.