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Watlow® duct heaters are constructed of sturdy 0.430 in. (11 mm) diameter WATROD™ heating elements mounted to a 1⁄4 in. (6 mm) thick steel flange. These air duct heaters are easily adapted to many non-pressurized air-heating systems.

Duct heaters are easily installed in applications requiring a wide range of temperature versus air flow combinations.

The modular duct heater offers increased reliability. The individual modules are removable through the housing of the assembly, which eliminates the need to pull the complete heater from the ductwork. This reduces downtime costs because the heating elements can be replaced individually. Performance improvements include quicker response time and reduced infiltration from the air stream being heated into the electrical enclosure.

Watlow air duct heaters offer advantages over gas or oil fired and open coil electric units with:

  • Installation flexibility—no flues or fuel lines
  • 100 percent energy efficient—no energy loss up the flue
  • Universal availability of electricity
  • Resistance coil in sheath is protected from corrosive environments

Duct heaters with general purpose enclosures meet UL® and CSA component recognition to 480 and 600VAC maximum respectively—UL® and CSA file numbers are E52951 and 31388.


Material Maximum Operating Temperatures Maximum Watt Densities
°F °C W/in2 W/cm2
Alloy 840  1200 650 30 4.7
  • Watt densities to 40 W/in² (6.2 W/cm²)
  • Recommended process temperatures from -20 to 1200°F (-7 to 650°C)
  • Wattages up to 225kW
  • Voltages up to 600VAC


  • Drying ovens
  • Autoclaves
  • Furnaces
  • Load banks
  • Heat treating
  • Reheating
  • HVAC
  • Paint drying

Features & Benefits:

Features Benefits
Long life Alloy 800 sheath
  • Resists corrosion/oxidation while protecting resistance coils against contamination
MgO insulation filled elements compacted to rock hard density
  • Maximizes dielectric strength, heat transfer and life
Field replaceable heating elements
  • Permits easy service and reduces downtime. Element change-out is made simple by a single screw clamp (D SERIES only)
3 1?2 in. (90 mm) thick mineral insulation
  • Keeps wiring cooler and reduces heat loss
  • Protects elements against moisture and other containments
General purpose terminal enclosure
  • Offers easy access to wiring 1?4 in. (6 mm) inside diameter thermowell
  • Accepts an optional Type J or K thermocouple for accurate sheath temperature sensing (D SERIES only)
Rigid stainless steel supports
  • Prevents element sagging or deformation in various mounting positions
1?4 in. (6 mm) thick steel flange with 3?8 in. (9.5 mm) diameter mounting holes
  • Easily bolts to the duct wall
WATROD hairpins are repressed (recompacted) after bending to assure MgO density
  • Eliminates hot spots and electrical insulation voids
Silicone resin seals
  • Rated to 221°F (105°C)