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WATROD and FIREBAR Circulation Heaters 

Circulation heaters provide a ready-made means to install electric heating with a minimal amount of time and labor. This is accomplished by combining heating elements, vessel, insulation, terminal enclosure, mounting brackets and inlet and outlet connections into a complete assembly.

Made from NPT screw plug or ANSI flange heater assemblies mated with a pressure vessel (tank), circulation heaters are designed to heat forced-circulation air, gases or liquids. Ideal for either in-line or side-arm operations, these assemblies direct fluids past FIREBAR® or WATROD™ heating elements, to deliver fast response and even heat distribution.

Watlow® meets virtually all your circulation heater assembly needs with made-to-order units. These units can be made from a wide range of heating element sheath materials, wattages, vessel sizes and materials, pressure ratings, terminal enclosures and controls.


Material Maximum Operating Temperatures Maximum Watt Densities
°F °C W/in2 W/cm2
Alloy 800/840  1600 870 120 18.6
316 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 three megawatts
  • UL® and CSA component recognition to 690VAC
  • Ratings to ANSI Class 600 pressure class
  • Alloy 800/840 sheath temperatures to 1600°F (870°C)
  • Passivated 316 stainless steel sheath temperatures to 1200°F (650°C)
  • Steel sheath temperatures to 750°F (400°C)


  • Deionized
  • Demineralized
  • Clean
  • Potable
  • Process
  • Industrial water rinse tanks
  • Hydraulic oil, crude, asphalt
  • Lubricating oils at API specified watt densities
  • Heat transfer oil
  • Paraffin
  • Caustic cleaners
  • Nitrogen, hydrogen and other air/gas systems
  • Superheating steam

Features & Benefits:

Features Benefits
Catalog screw plug and flange part numbers
  • Provides a wide selection of WATROD and FIREBAR elements to meet specific application requirements
ANSI B16.5 Class 150 on 4 or 6 inch FIREBAR element flanges and 3 to 14 inch WATROD element flanges
  • Meets recognized agency standards
FIREBAR assemblies pack more wattage in a smaller heater bundle
  • Replaces larger flanges with round tubular elements, with a smaller package
Compacted MgO insulation filled elements
  • Maximizes dielectric strength, heat transfer and life
1 inch (25 mm) thermal insulation rated to 750°F (400°C)
  • Reduces heat loss from the vessel
Heavy-guage steel jacket (shroud)
  • Protects thermal insulation and heating vessel and comes with protective primer coating
All catalog units rated to ANSI pressure Class 150
  • Provides pressure vessels (tanks) that are either carbon or 316 stainless steel
Standard offering includes units rated for up to and including ANSI pressure class 600 (application review required)
  • Provides pressure vessels (tanks) available in carbon steel, 304 or 316 stainless steel materials
  • Includes schedule 40, standard and 80 pipe used in the pressure vessel construction

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Related Literature

Specification Sheets (5)

User Manuals (1)

Quality Certificates (2)

Catalogs (4)



WATROD and FIREBAR Circulation Heaters
WATROD and FIREBAR Circulation Heaters
WATROD and FIREBAR Circulation Heaters
WATROD and FIREBAR Circulation Heaters