Horizontal heater treaters are used in the oil/gas industry to help facilitate oil/water separation by speeding up emulsions separation through applying heat. Heater treaters can be thought of as low pressure, three phase separators equipped with fire tubes. They separate gas from the incoming emulsion and separate the emulsion into a water phase and an oil phase. Heater treaters can also function as a free water knockout, a heat exchanger, a filter, and as a water wash tank.