The line heater is used to maintain or increase the temperature of a process stream. For gas, this may include keeping the gas above its hydrate temperature (freezing temperature). It typically consists of three elements, the liquid bath, fire tube, and process coil. The process coil may consist of two sections separated by a choke. The two coil sections are referred to Preheat and Postheat or Expansion. With this type, the gas is preheated then pressure is cut via the choke and the gas expands into the postheat section. This arrangement increases the efficiency and reduces the overall size. The heat source is most generally a natural draft gas fired firetube but could also be a forced draft burner or immersed electric elements.