Electric Duct Heater


Emerald provide a range of electric heater battery and controllers to suit most air conditioning and ventilation applications. Sheathed elements provide a clean and safe method of air heating. These heaters are intended for use in application where the air leaving temperature is below 400C( 70% RH db).

The Heaters are available in 3 model types.

Circular Duct Heaters

Comprises of a circular duct section manufactured from 0.9mm or 1.2mm galvanized sheet steel to suit ISO standard spiral ducting from 100mm to 500mm diameter with a factory fitted galvanized sheet steel terminal box. Element banks have been sized to give a range of steps and phases to suit the heating load requirements. The heater can be connected to the ducting system utilizing fast clamps.

Square & Rectangular Duct Heaters

Comprises of a square or rectangular duct section manufactured from 0.9mm or 1.2mm galvanized sheet steel with 25mm Duct mate flanges fitted where width or height is less than 600mm or a total perimeter of 1800mm and 35mm Duct mate flanges where greater than 600mm, or 1800mm perimeter. Flanges are fitted to both ends of the duct section. The duct sections are factory fitted with galvanized sheet steel terminal box and element bank sized to suit duct section, kilo wattage, steps and phase for the heating load requirements. For servicing and inspection purposes the complete terminal box with element bank can be easily removed from the housing without dismantling the duct work.


Stab-in Duct Heater

Comprises a galvanized sheet steel terminal box and a bank of elements sized to suit duct the required section with Kilowatts, steps and phase to suit the heating load requirements. Available capacity from 1KW to 50kW power supply 220V(Single Phase) & 440V. (Three Phase) in Different Banks.


Elements are constructed from Nichrome 5 spiral resistance wire surrounded by magnesium oxide power and sheathed in stainless steel, Copper pipe duly chrome plated evenly spread over the open area of the duct and secured into the terminal box. The elements are either linked with a copper bushbar or fitted with a terminal as required to achieve step and phase control requirements.

Heaters are designed to have a black heat surface temperature of 4000c at an air velocity of 2.5m/s




Fabricated out of 16G CRC Sheet duly powder coated having following controls. Panel is attached with heater battery & Internally wired with heater.

Front Panel Controllers.

1.        Fan on/off heater rocker switch.

2.         Power on indication.

3.         Heater on indication.

4.         Manual/auto rocker switch

5.         Fan run indication.

6.         Fan failure indication

7.         Door inter lock system


1.         Electric heater battery.

2.         Supply fan.

3.         Temperature sensor via duct or room thermostat.

4.         Airflow switch(normally open)

5.         High temperature cut-out (an integral part of a heater battery)

High Temperature

A high temperature cut-out is provided to protect the system and element bank against temperatures in excess of the design conditions and wired in series to ensure that the heater is shut down until the fault is rectified.

Manual Reset

This is manually reset when the fault has been rectified.

Auto Reset

This type of reset is designed to automatically reset when the heater has cooled to a predetermined level, it is therefore essential that when the cut-out has operated the heater remains electrically isolated and a visual and / or audible alarm is provided..

Any tripping out of the heater must be investigated and the cause rectified before the heat is reset.

The standard electric heaters are suitable for horizontal mounting as standard. Please advise if the heater is to be vertically mounted so that the high temperature cut-out can be selected to suit this application.


A run on timer must be incorporated into the control system to allow the fan to run on after the heater has been switched off to dissipate any residual heat.

Heater Selection

Calculate heater duty

Output=air volume x constant x temperature rise

Kw=m3/ s x 1.25 x ^t0c

Order Details

When ordering please state the following information

1.         Type of heater- Circular, Duct Mounted, or Stab-in

2.         Air Volume(m3/s)

3.         KW Loading

4.         Electrical Supply (220 to 240)V 1Ph or (380 to 415)V 3Ph

5.         Number of Steps

6.         Duct Size-Width x Height or Diameter(mm)

7.         Vertical Airflow if Required

8.         Any Special Requirements

Care must be taken when positioning the heater to prevent any damage or overheating of any other equipment in the system.


It is the responsibility of the final installation or commissioning person on site to ensure that all safety control interlocks function correctly and to shut down systems or part systems as designed to do so, within several seconds of activation.


Maximum Leaving Air Temperature                 400C

Maximum Element Temperature                        4000C

Maximum Air Velocity                                               6m/s

Voltage                                                                                (220 to 240)V 1Ph or (380 to 415)V 3Ph

Three Phase Connection                                          Star connection 3 wire for step control or 4 wires for

                                                                                                 thyristor control

Electrical Testing                                                           Flash Tested at 1750 volts for 2 seconds.

Insulation Test                                                                1 Meg Ohm Minimum



1.       Always fit an isolator for maintenance of the heater.

2.       It is important that all electrical connections are properly made. Elements are tested prior to dispatch and are within a tolerance of +-71/2  W. If the  elements are found to be faulty they can be easily removed and replace. Elements stored in dap conditions may need drying to attain correct insulation readings.

3.       Supply to heater should be 1ph or 3Pgh with Separate neutrals-Refer to nameplate.

4.       Cables should be silicone rubber, Fiberglass or similar high temperature insulated type and be installed.

5.       The heater is fitted with a high temperature cutout which has NC(normally closed) terminals. This must be connected in series with the main contractor coil circuit, to isolate the heater in the event of over-temperature(i.e. airflow failure).

      6.  Ensure sufficient earth connection to terminal provided.



Specification | Design May be change without any prior Intimationn