Water temp will be your biggest concern.
Check the limits of the PEX you want to use then check the temp at the back of your stove. Will the glycol overheat the PEX?
Do you have excess heat to transfer into the glycol?
Think about how you will deal with all the various situations; most notably, stove working but no need for heating water. What would happen to the heat transfered into the glycol?
Would you be better off with a fan?