Honeywell THX9321 Prestige 2.0 System Installation Manual page 19

Heat pump with outdoor temperature lockouts
Outdoor temperature lockouts are optional. See Installer Setup
options (ISU 3120).
Backup heat allowed to run with heat pump
Heat pump with backup heat as needed *
* 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.
Backup heat NOT allowed to run with heat pump
Heat pump or backup heat operates *
* 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.
Heat pump and backup heat operation
Backup Heat Type
Electric forced air
Gas or oil forced air
Hot water radiant heat
Hot water fan coil
Other
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).
When the Backup Heat is fossil fuel, the Geothermal Forced Air Heat turns off when the Backup Heat turns on. Geothermal Radiant
Heat stays on when the fossil fuel Backup Heat turns on.
When the Backup Heat is electric, Geothermal Radiant Heat and Geothermal Forced Air Heat stay on when the electric Backup Heat
turns on.
To turn off Radiant Heat during the shoulder seasons, install an outdoor reset control and connect to the Radiant Heat or
switch the thermostat to Emergency Heat mode.
Heat pump only
Backup heat only
Heat pump only
Backup heat only
Backup Heat Operation
Allowed to run with heat pump
NOT allowed to run with heat pump
Allowed to run with heat pump
Selectable in installer setup
Selectable in installer setup
THX9321/9421 Prestige
(see table below)
(see table below)
19
IAQ and RF EIM
®
Backup heat lockout
Compressor lockout
Backup heat lockout
Compressor lockout
Backup Heat Fan Operation
Thermostat controls fan
Equipment controls fan
[n/a]
Thermostat controls fan
Selectable in installer setup
69-2490—05