Screw Plug Immersion Heaters

screw plug immersion heaterWhat is a Screw Plug Immersion Heater? Screw plug immersion heaters are a specific type of immersion heater also sometimes referred to as immersion heaters for water are ideal for direct heating by immersion of liquids and processes including all types of oils and solutions involving the transfer of heat.

Watlow Immersion Heaters

These types of heaters are available in a wide assortment of sizes, screw plug immersion heaters by Watlow® 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 the elements particular sheath and plug material compatibility. Terminal enclosures are standard; but custom moisture resistant or explosion resistant enclosures are also available based on your individual needs or your specific application. Optional thermostats provide convenient and easy process temperature regulation to the screw plug immersion heater.

Common Types of Screw Plug Immersion Heaters

Common types of screw plug immersion heaters include:

  • Standard screw plug heater
  • General purpose hot water tank heater
  • Self contained screw plug heater

Screw Plug Heater Sheath Materials

screw plug heaters

Sheath materials for these types of heaters include Incoloy 800, 316/316L stainless steel, 304/304L stainless steel, copper, and steel.

Screw Plug Component Materials

Common screw plug materials for these immersion heaters include brass screw plug, 304 stainless steel, 316 stainless steel, and steel.

In addition to screw plug immersion heaters, Hi-Watt Inc. carries a wide variety of other types of immersion heaters including over the side immersion heaters, and flanged immersion heaters. Contact us today for more information on industrial heaters and industrial electric heaters and how we can help you.


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 wide variety of element sheath and screw plug materials
  • Meets a wide variety of application needs unique to your situation
Integral thermowells
  • Provides convenient and easy temperature sensor insertion and replacement without needing to drain the fluid being heated
Terminal enclosures
  • Provides the convenient ability to be rotated to simplify it’s connection with existing conduits
Welding or brazing WATROD and FIREBAR elements to the screw plug
  • Provides a leak free pressure tight seal
WATROD hairpins are repressed (recompacted)
  • Maintains MgO density, dielectric strength, heat transfer and life duration
2 ½ in. (64mm) NPT screw plug assemblies feature element support(s)
  • Ensures proper spacing for maximizing the heater’s performance and life

Screw Plug Heater Specifications

  • 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)

Thermostat Options

Thermostat options for screw plug heaters typically include stainless steel thermowells or plain steel thermowells. A stuffing box assembly can also be used as an alternative to a thermowell when the sensing bulb is directly immersed in a solution or liquid. This is used to seal the thermostat capillary for effective and efficient heating.

Immersion Heaters for Water

Hi-Watt carries the most extensive inventory of immersion heaters for water in the US. We are leading Watlow distributors and carry a wide variety of Watlow heaters. Contact us today for more information on screw plug immersion heaters.

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