Variacs are a variable tap auto-transformer and they don't waste a lot of energy as heat - they just feed the heating element 30V or 75V instead of the full 120V or 240V (depending on the model), each notch bumps it up 2 or 3 volts...
Warning: They are Not Cheap if you go buy one new, especially the larger ones that can handle a full 20A load. Look for surplus.
That'll give you rough temperature control and get the heat in the right neighborhood - especially useful if you've got a pan of wood chips directly over the heating element, and you don't want it to burst into flames every time the heating element cycles on...
Then you hook up the Programmable Temperature Control to cycle the power between the Variac and the element, and give you the spot-on temperature you want. It cycles the element at 80% duty cycle between dull red and off, rather than 20% duty cycle between Full On and Nothing - and often overshooting the target temperature in big swings.
