Spec Sheet

THX9321 PRESTIGE
®
2.0 AND THX9421 PRESTIGE
®
IAQ WITH EIM
68-0311—07 98
differential is set to 2 °F (1.0 °C), the indoor
temperature must be 2 °F (1.0 °C) away from the
setpoint before the backup heat turns on.
NORMAL OPERATION
When the Backup Heat Differential is set to Comfort, the
thermostat uses backup heat as needed to keep the indoor
temperature within 1 °F (0.5 °C) of the setpoint.
When the Backup Heat Differential is set to 2 °F or higher,
backup heat is not used unless the indoor temperature
drops to the Backup Heat Differential setting or the
Backup Heat Upstage Timer expires, whichever occurs
first. The upstage timer starts when the highest stage of
the previous equipment type turns on.
MANUAL TEMPERATURE CHANGE
When the Backup Heat Differential is set to Comfort, the
thermostat uses backup heat as needed to keep the indoor
temperature within 1 °F (0.5 °C) of the setpoint.
When the Backup Heat Differential is set to 2 °F or higher,
if the primary heat is making progress as expected,
backup heat will not be used to reach the new setpoint. Set
to a higher number to use less backup heat (a greater
difference between the current indoor temperature and
the new setpoint is required to turn on backup heat). See
notes below.
PROGRAMMED RECOVERY
If the primary heat is making progress as expected,
backup heat will not be used to reach the setpoint of the
next program period. Backup heat is always restricted
during a programmed recovery when the Adaptive
Intelligent Recovery feature is used. See note below.
NOTE: During a programmed recovery (or when the tem-
perature setpoint is changed by the user), the
thermostat waits to turn on the backup heat
depending on system performance, load condi-
tions and how many degrees the temperature set-
point is changed. Backup heat will be used ONLY
when the temperature is not rising quickly
enough to reach the setpoint in a reasonable
time.
NOTE: If the backup heat was used in the last 2 hours
because the primary heat was not able to main-
tain the setpoint, the thermostat may turn on the
backup heat earlier when the user raises the set-
point. This does NOT apply to heat pumps with
fossil fuel backup heat.
TO CHANGE BACKUP HEAT DIFFERENTIAL (DROOP)
SETTINGS
1. Select Advanced Options or Basic Options to
view/adjust Backup Heat Differential settings.
Fig. 196.
2. Default is Comfort. Adjust differentials as needed.
Fig. 197.
Backup Heat Holdoff Timer
Fig. 198.
The Backup Heat holdoff Timer is available for any system
with 2 heating types, the Backup Heat Differential is set to
2 °F (1.0 °C) or higher, and backup heat upstage timer is
set to 30 minutes or higher. Unlike the upstage timer, the
holdoff timer can be activated by a temperature set point
change (not limited to steady state). The holdoff timer
starts when the highest stage of the previous equipment
type turns on. The out-of-box setting is “Auto” and the
thermostat will hold off the use of backup heat as long as
possible when the set point is changed. If this is changed
to a setting other than auto, then the auxiliary heat will be
FORCED to turn on after this time is met.