What I'm suggesting is an element that, like INSL, won't change temperature on its own. However, it will still affect the surrounding temperature. It will spread heat to other elements, and take heat from them, but its temperature won't actually change. (Yes, I know this is impossible in real life, but so are many things in TPT.) This can be very useful if you want to heat or cool something to a specific temperature without having to worry about equilibrium or deal with the lack of precision provided by LIFE-based heaters/coolers.

Perhaps there could be two varieties of this element: one that "conducts" heat at a normal rate, and another that instantly sets the temperature of whatever it touches to its own temperature.

Oh, really? Had no idea.

Happen to know why it's been rejected?