that is maintained by the heater's thermostat.
For example, if you set the temp at 72, the temp at which the heater turns on will be a couple of degrees less than 72, and the temp at which the heater turns off will be a couple of degrees higher than 72.
I like to have the fan running all the time, as I think the moving air makes the thermostat maintain a more even swing range of temp.
The entry door has a built-in ventilation draft, and the plastic snap hinge needs to be closed to stop that draft. That complicates things a bit.
With this all in mind, you can test and find out what works better for you.