Duct Air Heaters

----Air-Heaters-Duct.jpgDurex Industries manufactures standard and custom designed process duct air heaters that are well suited for the needs of many heavy duty industrial applications. Incoloy® tubular heater elements for long life and durability. We construct high tensile strength cages to support heater elements in larger, higher temperature units to ensure proper air heater performance. The optimal sheath material and maximum allowable watt densities are used to minimize size, weight, and footprint. Replaceable heating element designs, as well as modular "bank" type designs, are available.

Medium temperature air heaters are for more economical, lower temperature applications to 750°F (400°C).
High temperature air heaters are designed for high process temperature applications to 1200°F (650°C).

Design Features:

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Duct air heater specifications & options

Construction Options

Process Sensors - thermocouple or RTD sensor probe is inserted into a thermowell in the heater to measure duct air outlet temperature. Type J and Type K thermocouples and Pt 100 Ω DIN Curve RTD sensors are the most common used. Standard sensor lead length is 72” (1825mm). Specify sensor type and lead length when ordering.

High Limit Sensors - A thermocouple or RTD sensor probe is fed through the mounting flange and clamped directly to a heater element. This allows for early detection of element over temperature conditions that may shorten heater life. An alternative is to insert the high limit sensor into a thermowell that is clamped or welded to the heater element sheath. This facilitates easy sensor replacement, but at the expense of a slower sensor response time. Standard lead length is 72” (1825mm). When ordering, specify sensor type, sensor mounting style and lead length.

Custom Voltage and Power Rating - A large variety of standard high-temperature and medium temperature duct air heater designs are available. However, custom volts, watts and watt density designs are available upon request.

Duct Configuration and Plate Flanges - In addition to the standard duct heater designs, Durex will custom design and fabricate purpose-built duct heaters to fit virtually any duct size and mounting flange requirements. Standard mounting flanges are carbon steel, however, 304 stainless steel and 316 stainless steel are readily available alternatives. Support rods, element support spacers and insulation collar are all of stainless steel construction standard.

Replaceable Heater Elements - Durex standard design duct air heaters use seal-welded heater elements. Optional replaceable heater elements can be specified with retaining clips or gas-tight compression fittings. Retaining clips keep elements in place and allow easy replacement in minimal pressure applications. Compression fittings offer field replacement, while still providing a gas-tight seal. Contact Durex for assistance in specifying replaceable elements.

Seal Options

Silicone Conformal Coating – On standard heaters, this seal provides general moisture / contamination protection to 220°F (105°C). However, it is porous and will allow moisture penetration over time. Not recommended for storage or use in high humidity environments.

Silicone RTV – Offers improved moisture and contamination protection to 400°F (200°C). However, it is also porous and will allow moisture ingress over time.

Epoxy Seal – Offers the best moisture and contamination protection of these seal choices. Rated for 450°F (230°C), this seal has low porosity and is recommended for higher temperature applications, high moisture environments and where long term storage is foreseen.

----SPST-DPST-Thermostats.jpgThermostats - Single pole (SPST) and double pole (DPST) available. Optional knob & bezel. Single pole, single throw (SPST) thermostat



Part numbers are for thermostats only. Please contact Durex Industries if knobs and bezels are required.


Part Number Description Maximum Voltage Maximum Amperage Bulb Length Bulb Diameter Capillary Length
CNTR-TSTAT-CAP-0-100-01 0-100°F SPST 240V 20 A 3.3" .24" 36"
CNTR-TSTAT-CAP-85-230-1 85-230°F SPST 240V 20 A 3.3" .24" 36"
CNTR-TSTAT-CAP-120-570-1 120-570°F SPST 240V 20 A 3.5" .20" 36"
CNTR-TSTAT-CAP-0-100-03 0-100°F DPST 480V 10 A / pole at 480V

30 A / pole at 240V
4.5" .375" 84"
CNTR-TSTAT-CAP-060-250-04 60-250°F DPST 480V 4.5" .375" 60"
CNTR-TSTAT-CAP-100-550-01 100-550°F DPST 480V 4.5" .375" 60"

How to Order

  • Quantity
  • Electrical Rating - Voltage, phase, wattage
  • Duct Size - Provide interior duct height and width dimensions
  • Duct Heater Configuration - High temp or medium temp duct heater design
  • Flange Size and Material - Provide information or advise if Durex to provide
  • Element Diameter and Quantity - If known or indicate Durex should provide
  • Element Watt Density - 20, 23, 30 W/in2 or indicate if Durex should provide
  • Dimensional Information - Refer to high temp or medium temp for required dimensions.
  • Seal Type - Silicone conformal coating (standard), RTV or epoxy.
  • Electrical Enclosure - NEMA 1(standard) or NEMA 4 (moisture resistant)
  • Sensing & Control - None (standard), process sensor type or/and high limit sensor type
  • Other Custom Specifications - Specify as required

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High Temperature Heater Design Features:

  • 5 to 300 kW Ratings at up to 480V
  • 1200°F (650°C) Max. Outlet Temperature
  • Up to 20 W/in² Rating
  • Insulated Stand-Off Housing for Cool Wiring Temperatures

View Standard Designs



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Medium Temperature Heater Design Features:

  • 5 to 60 kW Ratings at up to 480V
  • 750°F (400°C) Max. Outlet Temperature
  • Up to 15 W/in² Rating
  • Enclosure-Side Insulation for Cool Wiring Temperatures

View Standard Designs




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Typical Duct Air Heater Applications

  • Industrial Drying & Curing
  • Heat Treating
  • Reheating & Dehumidifying
  • Autoclaves
  • Convection furnaces
  • Core & Refractories Drying
  • Load Banks

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Process Heater Brochure PROC-BROC-0912 - 7MB


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