Flange immersion heaters are easy to install and maintain. ANSI Flange immersion heaters are designed for heating liquids and gases in tanks and pressure vessels and are ideal for applications requiring higher power levels. The Watlow flanged immersion heater is made with WATROD or FIREBAR tube elements that are brazed or welded to the flange. Stock flange heater with universal junction box. Flanged immersion heaters with FIREBAR elements also meet the requirements for high power liquid immersion applications in small tanks. The FIREBAR element's unique flat surface geometry enables it to deliver greater power and lower watt power density in smaller bundles, making it particularly suitable for petroleum liquid heating applications.