Immersion heaters Screw-on immersion heaters are made of copper, stainless steels or incolloy heating elements, brazed or welded on assembly plugs, with metric or British thread sizes.They are used for heating static or circulating water, oils or specific liquids, air or gas, at a maximum operational pressure of 15 bars. Power ranges from 100 W to 35 kW, for 230–380 or 690V or other specified voltages. ATEX certified products are available for explosive atmospheres