The total amount of heat generated by this circuit is
where Vcc is the 12 Volts from the power supply and
IRes is the current through the load resistor (R2).
This current is controlled by the input signal Vin.
Some of that heat is generated by the transistor WTrans,
the rest by the load resistors WRes.
If Vin = 0 there is no power dissipated and no heat generated.
If Vin = Vcc/2 (6V),
WTrans is about equal to WRes.
As Vin approaches Vcc, WRes rises and WTrans falls.
Clearly we want to operate in the region where Vin > Vcc/2, so that most of the heat generated is generated by the load resistors.
If the base resistance R1 is 0, the circuit is quite independent of the
transistor's gain. This graph was generated for Rbase = 0, Rload = 25. If Vin is around 10 V, then the transistor dissipates about 1 W, and the heating resistor about 4 W.