0191 5166636 enquiries@ht-uk.com

Screw plug immersion heaters are 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 Operating 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
  • 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)


  • Deionized water
  • Demineralized water
  • Clean water
  • Potable water
  • Process water
  • Industrial water rinse tanks
  • Vapor degreasers
  • Hydraulic oil, crude, asphalt
  • Lubricating oils at API specified watt densities
  • Air and gas flow
  • Caustic solutions
  • Chemical Baths
  • Anti-freeze (glycol) solutions
  • Paraffin

Features & Benefits:

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
2Ā½ in. (64mm) NPT screw plug assemblies feature element support(s)
  • Ensures proper spacing for maximizing heater performance and life