The idea of an element that can store any given quantity of thermal energy has always been interesting, but the fiddly bit is how exactly you intend for heat to transfer back and forth.

I'd personally prefer it if an element like this simply had an impossible amount of energy absorbtion ability, and transferred heat like normal. Its base temperature would rise according to the amout of energy it has absorbed.

For example, a block of heat element as such sitting next to 10000 temperature element would at first be 0 temperature, but absorb heat from the element according to base diffusion.

As the heat element absorbs heat, it substracts temperature from its own heat to add to a variable that is stored in the particle. As this variable increases, a simple proportion equation determines whether the heat element's temperature is too high or too low. If the temperature is too high, it subtracts from its heat and adds more to the variable.

If it is too high, the element subtracts from the variable and adds to its own temperature.

As a result, the element would be able to absorb -any- amount of heat depending on the size of the variable's cap. It could be ten times normal heat latency. A hundred times. But the actual heat of the element would never exceed the maximum temperature possible, since at this point, it has both reached its maximum possible latent heat as well as maximum 'actual' temperature.

So if you heated it up all the way, you could use it to boil water for like, an hour. You know? o.o And only one element is required, you can use heat switch to regulate it.