This KB notes the Surveyor MKII - SN230 PTZ camera heater operation temperatures.
This info is not in the specification.
Heater operation temps for the Surveyor MKII camera:
The simple answer on this is at about -1C / 30.2F of the outside / environment temperature the heater will start to work.
The more complete answer are related to a few factors as explained by Engineering.
1- The temperature inside of the dome is higher than the outside / environment temperature.
2- When the inside temperature drops to 15 C / 59F , the outside / environment temperature is then found to be around -1C / 30.2 F and the heater inside of the dome will come on.
3- When the inside temperature reaches 20 C / 68 F the heater will shut off.
4- Again, as the inside temperature drops gradually ( heater is off at this point )
and drops to 15C / 59F, the heater will come on.