First type (340K - applicable to coal slurry formula)
Simple control that only requires two redstone dust and one piston, temperature around 359-362.
The second type (extreme temperature control - applicable to liquid polyethylene)
Both device temperatures are controlled at around 765-769
Figure 1 (a redstone alloy wire placed on a redstone block)
Figure 2 (redstone torch plus two redstone dust)
Third type (Magic heater - suitable for 1400K temperature formula)