The boiler is controlled/turned on with an electric switch, which when turned on, opens a valve where the gas enters a combustion chamber. There is a continuous stream of natural gas via a pipe attached to the home’s gas main, usually from the street, that feeds a fire inside this chamber. Its electric ignition system is what lights these small jets of gas. The gas jets fire onto a heat exchanger connected to the water pipe carrying the cold water. The heat exchanger takes the gas-generated heat and heats the water, typically to around 140F (60C). The now-hot water is pushed throughout the home. An electric pump inside or very near the boiler keeps the water flowing through the loop of pipes and radiators.
Typically, boilers are categorized into different types based on their fuel type, working pressure and temperature, size and capacity, draft method, and whether or not they condense the water vapor in the combustion gases. Sometimes boilers are described by some by their key components, such as heat exchanger materials or tube design. The two main types of boilers are Firetube and Watertube boilers. In the former, the Firetube boiler, combustion hot gases flow through a system of tubes surrounded by water. In the latter, the Watertube boiler, water flows in the inside of the tubes, and the combustion hot gases flow around the outside of the tubes.