18 18-CD21D1-12
Installer’s Guide
TWINNING
These furnaces may be twinned. Twinning requires
that two furnaces with the same configuration, capac-
ity, and airflow must be used. They shall have common
returns with equal pressure drops or ducts with equiv-
alent lengths and sizes. See Field Wiring Diagrams be-
low for proper hookup.
TWIN
TWIN
R1
R1
TWINNING CONNECTION DIAGRAM
FOR TWINNING 1 STAGE FURNACES WITH
SINGLE WIRE TWINNING FEATURE
1 STAGE HEATING ONLY THERMOSTAT
1 STAGE HEAT
ONLY
THERMOSTAT
(WITH FAN SWITCH) FURNACE NO. 1
FURNACE NO. 2
BLOWER OPERATION OF
UNIT NO. 2 IS SYNCRONIZED
WITH UNIT NO. 1 VIA SIGNALS
FROM TWIN CONNECTION.
SEE NOTE 4
SEE NOTE 3
ISOLATION RELAY
(FIELD SUPPLIED)
SEE NOTE 4
ISOLATION RELAY
SEE NOTE 4
B/C
B/C
B/C
From Dwg. 21B341422 Rev. 3
TWIN
TWIN
R1
R1
TWINNING CONNECTION DIAGRAM
FOR TWINNING 1 STAGE FURNACES WITH
SINGLE WIRE TWINNING FEATURE
1 STAGE HEAT / 1 STAGE COOL THERMOSTAT
1 STAGE
HEATING / COOLING
THERMOSTAT FURNACE NO. 1
FURNACE NO. 2
BLOWER OPERATION OF
UNIT NO. 2 IS SYNCRONIZED
WITH UNIT NO. 1 VIA SIGNALS
FROM TWIN CONNECTION.
SEE NOTE 4
SEE NOTE 5
ISOLATION RELAY
(FIELD SUPPLIED)
SEE NOTE 4
ISOLATION RELAY
SEE NOTE 4
OUTDOOR UNIT
(NO TRANSFORMER)
OUTDOOR UNIT
(WITH TRANSFORMER)
RC
ISOLATION RELAY
(FIELD SUPPLIED)
SEE NOTE 3
B/C
B/C
B/C
From Dwg. 21B341423 Rev. 2