1. Pot boiler – this work similar with heating a kettle on the stove. Fire is provided and it heats up the bottom of the boiler along with the fluid in that area. Heat travels inside the boiler to obtain similar temperature for the fluid inside.
2. Fire-tube boiler – tubes with fire passing through can be found on the walls of the boiler to provide even heat to the fluid inside it.
3. Steam boiler – has similar configuration with the fire-tube boiler but instead of fire, steam or hot water is used in heating the fluid inside the vessel.
4. Flash tankless boiler – it is a special type of water-tube boiler that doesn’t need a storage tank to operate.
5. Combination of fire-tube boiler with water-tube fire box – this is a vessel that uses both the concept of fire-tube and water-tube boilers.
6. Sectional boiler – this is quite similar to water-tube boiler but instead of having water tubes, it has hot water along the cross-section of the boiler.