Screw plug heaters

Screw Plug Heaters

Screw plug heaters are a type of immersion heaters that can heat liquids and gases in a variety of applications.  They can be used to process water heating and freeze protection.  Heatrex offers many different screw plug heaters that can provide direct heating at an energy-efficient cost.


Screw plug heaters are used in wide variety of applications:

  • Water storage tanks
  • Cleaning and rinsing tanks
  • Warming equipment
  • Preheating oil
  • Food industry
  • Process air
  • Boiler equipment
  • Freeze protection

Screw plug heaters

Construction Feature

  • Heatrex’s screw plug heaters range from 1”- 2 ½”.
  • The element bends are repressed uniformly to ensure electrical insulation integrity.
  • There is one piece forging of the hex, thread and riser that assures reliability.
  • The element spacers help prevent any hot spots,  and the busing is permanent and encapsulated in an epoxy seal.
  • All catalog heaters are UL CSA labeled.  Please consult the factory for custom heaters.
  • Tubular Elements are welded or silver soldered into a hex head pipe thread fitting.  Elements have 80/20 nickel-chromium resistance coils centered in a heavy gauge metal tube surrounded by magnesium oxide insulation.  Through rolling, the magnesium oxide is compacted for rapid heat transfer from the coil to the sheath.  Elements are annealed, bent and then 360° repressed to ensure magnesium oxide integrity in the bent area.  1” and 1 ¼” screw plug heaters have .312” diameter elements for operation up to 277 Volts. 2”- 2 ½” screw plug heaters have .475” diameter elements suitable for operation up to 600 Volts.
  • Heaters can be furnished with a general purpose NEMA 1 terminal housing or a liquid proof NEMA 4 terminal housing.
  • Built-in thermostats can provide automatic temperature control without the necessity of installing a separate well for the thermostat bulb in the field and making electrical connections between the heater and control.  The thermostats adjust from 0-100/120°F, 40-120°F, or 60-250°F.  Standard thermostats are single-pole for single-phase heaters,  a  pilot duty thermostat for  three-phase applications,  and a two–pole thermostat for de-energizing load carrying applications.

Screw plug heaters

Heater Options

Here are a few heater options available:

  • Liquid Proof NEMA 4  thermal housing (Without Built-In Thermostat): Cast  box with threaded, gasketed cover and 1” NPT female threaded hubs for electrical connections.  For applications where there is danger of moisture entering the  terminal box.
  • Explosion Resistant Heater: Rated for Class I, Div. I, Groups B, C & D.
  • Liquid Proof NEMA 4  thermal housing(With Built-In Thermostat): Welded steel outlet box with enamel finish and gasketed cover.  Pilot light is visible through lens cover.  Two 1” NPT hubs provided for electrical connections.  Stainless steel outlet box is available as an option.
  • Single-Pole, Single-Throw Thermostat: Standard on all single phase heaters and all pilot duty applications.
  • Omit Outlet Box:  For applications where heater terminals will be protected by field-furnished enclosures.
  • Special Sheath Materials:  Incoloy 800, Inconel 600, Type 316 Stainless Steel and
  • Special Header Materials:  Incoloy 800, Inconel 600 and Type 316 Stainless Steel headers.
  • Vertical Mounting for 1 ¼”, 2” and 2 ½” Screw Plug Heaters with Thermostat:  Thermostat must be mounted vertically.  Heaters with single-pole, single-throw thermostats can be mounted in any position without relocating the box.
  • Other Special Ratings: 2 & 2 ½” NPT screw plug heaters available in any non-stock voltage up to 600 Volts.  All sizes available with lower watt densities for special applications.
  • Longer Elements: Consult factory for length and wattage limits per element.
  • UL/CSA Approval: Available on all  catalog heaters listed.
  • Longer Element Cold Ends: Cold ends are ¾” for copper, or 1-5/16” for stainless steel and steel.  In vertically mounted heaters and other applications where the liquid will not completely cover the elements, immersion length should be increased by the length of additional cold end.

If you would like to speak with a Heatrex representative, please visit to discuss about a screw plug heater.

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