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Electrical Requirements
Refer to attached wiring diagram and wiring diagram on
inside of cover. Make sure line and control voltage of
system matches that noted on wiring diagram.
Wire in accordance with N.E.C. and any existing local
codes. Check tightness of all factory and field electrical
connections. Make sure fan interlock is wired in if the
Duct Heater does not have an air flow switch.
Use 90°C (194°F) copper wire.
Control must be wired for N.E.C. Class 1 unless
otherwise specified.
When heater has integral transformer for control voltage
to thermostat, use thermostat with isolating contacts to
prevent interconnection of Class 2 outputs.
Disconnect all electrical power before servicing.
When servicing heater, make sure all components are
repositioned in the proper location and reconnected per
the wiring diagram.
Replacement parts must be identical to the original
components. Contact factory for replacement parts.
Minimum Air Velocities
The minimum uniform airflow in a duct heater is directly
related to the inlet air temperature. Consideration must
be given to both airflow across the heater and inlet air
temperature, (shown at left).
1. To calculate the watts per sq. ft. of duct area,
divide the total watts required by the duct
area.
EXAMPLE: Duct Size
Total watts
W/Sq. Ft.
2. If the air handler equipment is expressed in
fpm, then a direct cross reference can be
made by comparing the temperature of the air
(as it enters the Duct Heater) to the KW rating
on the chart of rated velocity.
a. Draw a line horizontally from the Watts/Sq.
Ft. required to the inlet air temperature being
used.
b. From this point of intersection on the Inlet Air
Curve, draw a line down vertically to establish
the air velocity.
c. The velocity should never be lower than the
velocity as determined from the chart. In
cases where this is not true, the velocity must
be increased or the KW required must be
reduced.
3. In cases where the air handling equipment
is expressed in CFM, convert to FPM by
dividing the CFM by the duct area.
EXAMPLE:
= 2ft. x 3ft.
= 20,000
= 20,000 = 3333
6
FPM
=
CFM
Duct Area
22,000
20,000
18,000
16,000
14,000
12,000
10,000
8,000
6,000
4,000
2,000
200
400
600
Minimum Air Velocity (fpm)
Note: Minimum airflow must be
maintained at any point over the face of
the heater.
Note: Observe at least one complete
heating cycle to insure that cycling of
the safety limit controls does not occur
before leaving the installation.
800
1,000
1,200
1,400
3
Electric Duct Heaters
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