(1) According to Tube Contents: Boilers can be water tube or fire tube type. In water tube boilers water flows in tubes and in Fire Tube Boilers hot flue gasses circulate through tube. Babcox and Wilcox Boiler is water tube boiler while Locomotive and Lancashire Boiler are the examples of Fire tube Boiler.
(2) According to Axis of Boiler: The Boiler can be a Horizontal axis or Vertical Axis type.
Babcox and Wilcox, Locomotive and Lancashire Boilers are the examples of Horizontal axis boilers.
(3) According to Number of Boiler tubes: May be single or multiple tubes boilers. Cornish Boiler is single tube boiler whereas other boilers are multi tube boilers.
(4) According to Position of Furnace: Externally or internally fired boilers. In externally fired boiler the furnace is external to boiler shell.
(5) Mobility: Stationary or Moving Boilers.
(6) Draught: Forced or induced draught.
(8) Utility of steam: Example: Power Plant, Marine and Locomotive boilers etc.