Bulletin 30-034.009
Copyright © 2022 Unico Inc.
Page 8
SPECIAL WIRING FOR HEAT PUMPS
When using a heat pump coil it may be necessary to
install an outdoor thermostat because the entering air is
set at 70°F (21°C) and the heater has an auto limit set at
165°F (73°C). The outdoor thermostat will prevent
short-cycling of the heater auto limit due to high
temperature air and will energize the 3
rd
stage. Refer to
Table 2 to determine if your system requires an outdoor
thermostat.
Table 2. When to use outdoor thermostat for last
stage furnaces
Airflow
kW Rating of Electric Furnaces
CFM (m
3
/s)
2
5
7.5
10
15
20
200 (.09)
N/A
N/A
N/A
N/A
300 (.14)
N/A
N/A
N/A
N/A
400 (.19)
N/A
N/A
N/A
500 (.24)
N/A
N/A
600 (.28)
N/A
700 (.33)
N/A
800 (.38)
900 (.42)
1000 (.47)
1250 (.59)
Outdoor thermostat not required
Use outdoor thermostat to limit last stage element
For units using the
Unico
Smart Control Board (SCB),
no outdoor thermostats are required. The
Unico
SCB
will lock out the third stage of the electric furnace when
the heat pump is on.
Figure 16. Control Wiring to the SCB
SEQUENCE OF OPERATION
All furnaces have a built-in delay feature to delay the
furnace from coming on before the air handler is
operating. There is no delay-off feature. As soon as the
thermostat is satisfied, the furnace de-energizes. For the
single speed air handlers with PSC motors, the blower
will also immediately stop. For the variable speed EC
motor and SCB, the air handler will ramp down for 45
seconds. An air pressure switch is in series with the fan
interlock relay for added protection and safety. The
larger furnaces have multiple stages with time-delay
sequencers for a softer start.
CAPACITY AT LOWER VOLTAGES
The elements are rated at 240 Volts and should not be
used at higher voltages. Lower voltages are acceptable.
However, furnaces are resistive loads so capacity is
reduced by the square of the voltage ratio.
kW (output) = kW (rated) x (V/240)
2
Note: (V/240)² = Factor
Example: For a WON0752-C Model: kW (output) = 7.2 x (230/240)2
kW (output) = 6.6kW
Therefore, multiply the rated capacity shown in Table 4
by the factor shown in Table 3 to determine the actual
output of the furnace at other voltages.
Table 3. Furnace Capacity Factor at other voltages
Voltage
Factor
240
1.00
230
0.92
220
0.84
208
0.75
200
0.69
Table 4. Rated Capacity for WON heaters
Model
L
inch
Rated Capacity
kW @240V
Amperage
@ 240V
WON0202-C
WON0502-C
13
13
2.0
4.8
8.30
20.00
WON0752-C
16
7.2
31.25
WON1002-C
16
9.6
40.00
WON1502-C
21
14.4
60.00
WON2002-C
24
19.2
80.00
WON0504-C
21
4.8
11.54
WON0754-C
21
7.2
18.04
WON1004-C
21
9.6
23.09
WON1504-C
21
14.4
34.64
