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THX9321 PRESTIGE
®
2.0 AND THX9421 PRESTIGE
®
IAQ 2.0 WITH EIM
68-0311—01 62
HEAT PUMP AND BACKUP HEAT OPERATION
Heat pump with outdoor temperature lockouts
Outdoor temperature lockouts are optional. See Installer Setup options (ISU 3120).
Geothermal Radiant Heat
The thermostat can be setup to control Geothermal Radiant
Heat, Geothermal Forced Air Heat and Backup Heat, all from
one thermostat. The thermostat stages the equipment starting
with the Geothermal Radiant Heat followed by Geothermal
Forced Air Heat and then Backup Heat as needed to maintain
the desired temperature. The thermostat allows you to set
differential temperature settings between each stage if you
want the equipment to stage a certain way (see ISU 3030 to
ISU 3090, page 22). For additional wiring diagrams, see
page 107.
NOTE: To turn off Radiant Heat during the shoulder sea-
sons, install an outdoor reset control and connect
to the Radiant Heat or switch the thermostat to
Emergency Heat mode.
Electric Backup Heat (Backup Heat Allowed
to Run with Heat Pump)
HEAT MODE
The thermostat turns on Backup Heat only when the indoor
temperature drops to the selected Backup Heat Differential
setting or the Backup Heat Upstage Timer expires (whichever
occurs first). Geothermal Radiant Heat and Geothermal Forced
Air Heat stay on when the Backup Heat turns on.
EMERGENCY HEAT MODE
The thermostat turns on the Backup Heat to maintain the
desired temperature setting. Geothermal Radiant Heat and
Geothermal Forced Air Heat are not used.
Table 4. Heat Pump and Backup Heat Operation.
Backup Heat Type Backup Heat Operation Backup Heat Fan Operation
Electric forced air Allowed to run with heat pump Thermostat controls fan
Gas or oil forced air NOT allowed to run with heat pump Equipment controls fan
Hot water radiant heat Allowed to run with heat pump [n/a]
Hot water fan coil Selectable in installer setup Thermostat controls fan
Other Selectable in installer setup Selectable in installer setup
Heat pump only
Heat pump with backup heat as needed *
Backup heat only
Heat pump only
Heat pump or backup heat operates *
Backup heat only
Outdoor temperatureOutdoor temperature
Backup heat lockout
Backup heat lockout
Compressor lockout
Compressor lockout
* No backup heat unless indoor temperature drops to selected Backup Heat Differential setting, or Backup Heat
Upstage Timer expires. Heat pump stays ON when backup heat turns on.
* No backup heat unless indoor temperature drops to selected Backup Heat Differential setting, or Backup
Heat Upstage Timer expires. Heat pump turns OFF when backup heat turns on.
Backup heat allowed to run with heat pump (see table below)
Backup heat NOT allowed to run with heat pump (see table below)