Heatrex custom manufactures TUBULAR & FINNED TUBULAR
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HVAC Electric Duct
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P.O. Box 515,
Meadville, PA 16335
Phone: (814) 724-1800
Fax: (814) 333-6580
E-mail: sales@heatrex.com
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Custom 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 KUB Custom Slip-in Open Coil Heater
    • Type PUB Custom Flanged Open Coil Heater
    • Type TFKU Custom Slip-in Finned Tubular Heater
    • Type TFPU Custom Flanged Finned Tubular Heater
  • Approvals - Heaters and panel boards (if required) shall meet the requirements of the National Electrical Code and shall be listed by Under writers 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 air stream 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  · Product Specification

Product Option


Non UL listed
UL listed


KUB (custom slip-in)
PUB (custom flange)

TFKU (custom finned tubular slip-in)

TFPU (custom finned tubular flange)

Control Options

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

Control K (SCR control)

Product Specification

Custom Options

“Heater On” pilot light
“Low Airflow” pilot light

Airflow switch for negative pressure operation

Bottom mounted terminal box

Built-in PE transducer

Controls mounted in remote panelboard

Custom terminal box NEMA 12 type

Custom terminal box NEMA 4 type

Custom terminal box UL3R type

Deletion of disconnect switch

Deletion of transformer

Deletion of transformer and contactor

Disconnecting contactors

Dust-tight Terminal Box

Each “Stage On” pilot light(s)

Fan Relay (in addition to Airflow Switch)

Fan relay (instead of airflow switch)

Fuses for heaters rated 48 amps or less

Insulated Terminal Box

Mercury controlling contactors (not available in all areas)

Pilot duty single stage duct thermostat

Pilot duty single stage room thermostat

Pilot duty two stage duct thermostat

Pilot duty two stage room thermostat

Proportional electronic duct thermostat with set point adjuster

Proportional electronic room thermostat

Protective screens

Special inputs (135 ohms, 2200 ohms, 4-20 mA, 0-10 VDC)

Step Controller

Transformer primary fusing


·  Custom HVAC Electric Duct Heaters Dimensional Drawing


Custom HVAC Electric Duct Heaters Special Applications
(PDF, 4000KB)

Custom Design Specifications - Open Coil
(PDF, 247KB)

Custom Design Specifications - Finned Tubular
(PDF, 274KB)

HVAC Electric Duct Heaters Troubleshooting Guide
(PDF, 26KB)

HVAC Electric Duct Heaters Slip and Drive Construction
(PDF, 90KB)

Type 3R Terminal Boxes
(PDF, 107KB)

Replacement Parts Order Form
(DOC, 78KB)

Electric Duct Heaters IOM
(PDF, 412KB)