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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