You will need to....1. control and....2. monitor the temperature.
A thermostat will control the temperature to a set temp. (Either shut off power when it hot and turn on power when it's cold or a really good one will pulse the power constantly) This is good. You may need/want an additional thermometer to monitor the temp.
A rheostat will limit the power to the heater (dimmer) which will require you to set it and check what temp results. You will need to adjust the rheostat to compensate for the ambient temp.
It's cheeper to get a rheostat (dimmer) and just monitor the temp but it's safer to get a good thermostat that will keep the temperature constant.
Hope this helps
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