System Installation Guide
20
69-2490—05
Backup heat differential and upstage timer
Basic and Advanced Temperature Control Options (ISU 3010)
A backup heat differential and backup heat upstage timer can be set on any
system that has more than one type of heating equipment. See installer setup
options (ISU 3070-3110).
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 set-
point.
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 set-
point.
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
restrict
-
ed during a programmed recovery when the Adaptive Intelligent Recovery feature
is used. See note below.
Basic Options:
The Installer Setup displays basic temperature control options
which include Backup Heat Differential, Backup Heat Upstage Timer and Outdoor
Temperature Lockouts. Note: Outdoor Temperature Lockouts only apply to Heat
Pump applications.
Advanced Options:
The Installer Setup displays both Basic and Advanced
Options. Advanced temperature control options include Finish With High Cool
Stage, Finish With High Heat Stage, Temperature Differential settings between all
stages and Cycle Rate settings per stage.
During a programmed recovery (or when the temperature setpoint is changed by the user), the thermostat waits to turn on the
backup heat depending on system performance, load conditions and how many degrees the temperature setpoint is changed.
Backup heat will be used ONLY when the temperature is not rising quickly enough to reach the setpoint in a reasonable time.
If the backup heat was used in the last 2 hours because the primary heat was not able to maintain the setpoint, the
thermostat may turn on the backup heat earlier when the user raises the setpoint. This does NOT apply to heat pumps with
fossil fuel backup heat.
Finish With High Heat or Cool Stage - When a multi-stage heating or cooling system is used, this feature keeps the high stage
of the heating or cooling equipment running until the desired setpoint is reached. Recommended setting for Geothermal Heat
Pumps to allow the loop to rest.
