Honeywell RTH4300B Manuel D'utilisation page 9

Select the fan setting About your new thermostat
Set FAN switch to choose whether the fan
runs continuously or only as needed.
Set the FAN switch to Auto or On.
In "Auto" mode (the most commonly used
setting), the fan runs only when the heating
or cooling system is on.
If set to "On," the fan runs continuously. Use
this setting for improved air circulation, or for
more efficient air cleaning.
M28316
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RTH4300B Programmable Thermostat
69-2226EFS—05