All boilers, whether hot water or steam, depend on fuel to run. The heating process is initiated when the burner heats or evaporates the water inside it, which is ultimately transported via pipe systems. Hot water boilers rely on pumps to move the heat through the system, while steam boilers are transported with the pressure generated in the heating process. Eventually, cooled water or condensed steam is returned back through the pipes to the boiler system so that it can be heated once again. While the boiler is generating energy in the form of heat, flue gases, a byproduct of this process, are removed through a chimney system - which is why regulating the emissions of industrial boilers is taken very seriously.