Which of the following is NOT a type of boiler discussed?

The answer indicates that "Gas Boiler" is not considered a type of boiler discussed in the context of the question. However, it's important to clarify that gas boilers are actually a recognized type of boiler commonly used in residential and industrial applications.

In the context of the options provided:

• Electric boilers utilize electricity to heat water and produce steam without the need for combustion of fossil fuels.

• Fire tube boilers are designed where hot gases pass through tubes surrounded by water, a common design for steam generation in various applications.

• Steam boilers specifically refer to those that generate steam for heating or powering machinery through a closed system.

Understanding the specifics of these types can give insights into their operational mechanisms and applications. Given this, when approaching such questions, it’s useful to focus on the definitions and functions of each boiler type in the material you are studying.