In a boiler system, what is the heat exchange medium?

• A. Steam
• B. Water
• C. Oil
• D. Gas

Answer: (B)

Water is the heat exchange medium. In a boiler, the hot combustion gases transfer energy to water circulating through the boiler tubes. Water absorbs this heat efficiently and, as it gains enough energy, it turns into steam; the water itself is the medium that carries heat from the burner to the steam that’s produced. Steam is the energy carrier produced by the boiler, not the fluid circulating to transfer heat inside the system. Oils or other fluids are not used as the standard heat transfer medium in a typical boiler.