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Meadville, PA 16335
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Open Coil HVAC Duct Heater

A job specification can be prepared by using the following information. Simply darken the applicable circles. Material which is part of the basic specification has already been darkened. Additional copies of this specification guide are available from your local Heatrex representative.
  • Duct heaters shall be Heatrex:
    • Type HUA Custom Slip-in Heater
    • Type HUP Custom Flanged Heater
  • Approvals - Heaters and panelboards (if required) shall meet the requirements of the National Electrical Code and shall be listed by Underwriters Laboratories for zero clearance to combustible surfaces and for use with heat pumps and air conditioning equipment.
  • Heating elements shall be open coil, 80% nickel, 20% chromium, Grade A resistance wire. Type C alloys containing iron or other alloys are not acceptable. Coils shall be machine crimped into stainless steel terminals extending at least 1" into the airstream and all terminal hardware shall be stainless steel. Coils shall be supported by ceramic bushings staked into supporting brackets.
  • Heater frames and terminal boxes shall be corrosion resistant steel. Unless otherwise indicated, the terminal box shall be NEMA 1 construction and shall be provided with a hinged, latching cover and multiple concentric knockouts for field wiring.
  • All heaters shall be furnished with a disc type, automatic reset thermal cutout for primary over temperature protection. All heaters shall also be furnished with disc type, load-carrying manual reset thermal cutouts, factory wired in series with heater stages for secondary protection. Heat limiters or other fusible over temperature devices are not acceptable.
  • Heaters shall be rated for the voltage, phase and number of heating stages indicated in the schedule. All three-phase heaters shall have equal, balanced, three-phase stages. All internal wiring shall be stranded copper with 105°C insulation and shall be terminated in crimped connectors or box lugs.
  • Terminal blocks shall be provided for all field wiring and shall be sized for installation of 75°C copper wire rated in accordance with NEC requirements.
  • Heaters shall be furnished either with the Control Option specified in the schedule and described below or with the specific components listed in the schedule.

Product Option


Non UL listed
UL listed


HUA (standard slip-in - quick ship available)
HUP (standard flange - quick ship available)

Control Options

Control G (contactor control)
Control J (pneumatic control)

Control K (SCR control)

Custom Options

Disconnecting Contactors (substitute for De-Energizing Contactors)
Dust-tight Terminal Box

Fan Relay (in addition to Airflow Switch)

Fan Relay (substitute for Airflow Switch)

Insulated Terminal Box

Mercury Contactors (substitute for De-Energizing Contactors, not available in all areas)

Pilot Lights "Heater On"

Pilot Lights "Low Airflow"

Pilot Lights "Stage On"

Remote Panelboard

Step Controller


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