Screw Plug Immersion Heaters

screw plug immersion heater

Screw plug immersion heaters are a specific type of immersion heater ideal for direct immersion heating of liquids, including all types of oils and heat transfer solutions. Available in a variety of sizes, Watlow® screw plug immersion heaters feature both WATROD™ round and FIREBAR® flat tubular elements.

Heating elements are hairpin bent and either welded or brazed into the screw plug —depending on element sheath and plug material compatibility. General purpose terminal enclosures are standard; with optional moisture resistant, explosion resistant and explosion/moisture resistant enclosures available to meet specific application needs. Optional thermostats provide convenient process temperature regulation to the screw plug immersion heater.


Material Maximum Opening Temperatures Maximum Watt Densities
°F °C W/in² W/cm²
Alloy 800/840 1600 870 120 18.6
Stainless Steel 1200 650 120 18.6
Steel 750 400 120 18.6
N/A 350 175 120 18.6
Features & Benefits:
A variety of element sheath and screw plug materials
  • Meets your application needs
Integral thermowells
  • Provides convenient temperature sensor insertion and replacement without draining the fluid being heated
Terminal enclosures
  • Provides ability to be rotated to simplify connection with existing conduits
Welding or brazing WATROD and FIREBAR elements to the screw plug
  • Provides a pressure tight seal
WATROD hairpins are repressed (recompacted)
  • Maintains MgO density, dielectric strength, heat transfer and life
2 ½ in. (64mm) NPT screw plug assemblies feature element support(s)
  • Ensures proper spacing for maximizing heater performance and life
  • Watt densities to 120 W/in² (18.6 W/cm²)
  • Wattages to 38 kilowatts
  • UL® and CSA component recognition to 480VAC and 600VAC respectively
  • Alloy 800/840 sheath temperatures to 1600°F (870°C)
  • Passivated 316 stainless steel sheath temperatures up to 1200°F (650°C)
  • 304 stainless steel sheath temperatures up to 1200°F (650°C)
  • Steel sheath temperatures up to 750°F (400°C)


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