To my limited knowledge, heaters look like a tube which is submerged into the water, but I have heard of fishes being burnt by heaters, so I have a few questions (annoying, I know. Sorry):
Firstly, will RES's get burnt by heaters?
Secondly, if I need to protect them from the heaters, what should I use (bought or DIY)?
Its possible but its more likely they might break the heater then get burnt by it. An easy solution is get some PVC pipe from a hardware store and drill holes in it. Depending on the size a soda bottle might even work. In one of my tanks I simply put the heater in a place the turtle couldn't reach.