Definition of thermic by Google:
adjective 1. relating to heat.
e.g. thermic effect
Definition of thermal by Google:
adjective 1. relating to heat.
e.g. thermal conductivity
Honestly, I also don't really understand what is thermal other than the vague definition "relating to heat"
"Thermal" is far more common as a separate word for concepts related to heat: thermal blanket, thermal reaction, thermal physics, thermal depolymerization, thermal power plant, etc.
You will see "thermic" used as a suffix in many scientific terms that relate to heat: endothermic, exothermic, hypothermic, exothermic and a few others.
They are the same. Although according to corpus of contemporary american English, I think you should use the word Thermal, because thermic is very unusual and has been used rarely.
