you CANNOT heat cells in a normal EU reactor then cool them in a coolant reactor to double dip on EU, if you heat a cell (or any componant for that matter) in a EU reactor it wont let you put it into a coolant reactor until it has lost all damage (heat) that was gained in the eu reactor. it even has a tooltip that says so, devs are way ahead of you there
Just tested and found this result. Came back on to delete my post but you beat me to it.