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• After 2 minutes, the IFC increases to 57% at a rate
of 1% per second
• After 10 total minutes, the IFC increases to 78% at a
rate of 1% per second.
• After 20 total minutes, the IFC increases to 100% at
a rate of 1% per second for the remainder of the call
for heat.
• The circulator is adjusted to the appropriate CFM,
corresponding to the current firing rate.
MIN.
50%
60%
(80%)
70%
IGNITION
10 MINS.
8 MINS.
2 MINS.
Operation with Conventional 2-Stage Thermostat
(DIP switch selects 2-stage heat)
Call for 1st-Stage Heat - Thermostat contacts close R to W1.
After a successful Light Off Sequence and expiration of the
Ignition Stabilization Period:
• The IFC adjusts to the low firing rate.
• After 2 minutes, the IFC increases to 50% fort he
next 8 minutes.
• Thereafter, the IFC will increase 10%, at a rate of 1%
per second, every 10 minutes for the remainder of
the call for heat (See above figure).
• The circulator is adjusted to the appropriate CFM,
corresponding to the current firing rate.
MIN.
50%
60%
(80%)
70%
IGNITION
10 MINS.
8 MINS.
2 MINS.
90%
Operation with Conventional 2-Stage Thermostat
(DIP switch selects 2-stage heat)
Call for 2nd-Stage Heat - Thermostat contacts close R to W1
and W2.
After a successful Light Off Sequence and expiration of the
Ignition Stabilization Period:
• The IFC adjusts to the low firing rate.
• After 2 minutes, the IFC increases to 80%.
• Thereafter, the IFC will increase 10%, at a rate of 1%
per second, every 10 minutes for the remainder of
the call for heat.
• The circulator is adjusted to the appropriate CFM,
corresponding to the current firing rate.
MIN.
50%
78%
(80%)
100%
IGNITION
2 MINS.
CALL FOR
2ND STAGE HEAT
UNIT CALL FOR HEAT ENDS
Call for 2nd-Stage Heat with 1st-Stage call for heat call in
progress, with conventional 2-Stage Thermostat.
• The IFC increases the firing rate to 100% at a rate of
1% per second for the remainder of the W2 call.
• The circulator is adjusted to the appropriate CFM,
corresponding to the current firing rate.
Call for 2nd-Stage Heat satisfied; Call for 1st-Stage Heat re-
mains.
• The IFC remains at the current firing rate until the
1st-Stage call for heat is satisfied.
HEATING O PERATION WITH CTK01AA THERMOSTAT
(COMMUNICATING)
• When the Thermostat Heat Setup DIP switch is set
to 2-Stage heat, the IFC operation will be compatible
with a CTK01AA communicating thermostat.
• When a call for heat is sent, the furnace will go through
the Light Off Sequence, at which time the Heat Current
Demand Status will still show 0%. After the successful
Light Off Sequence and expiration of the Ignition
Stabilization Period:
• The IFC adjusts to the low firing rate.
• After 2 minutes, the IFC accepts the specific Heat
Requested Demand.