Thorium Cell is the first among the heaters to produce heat in an area of effect. While all previous heaters transmitted heat only to the four cardinal directions adjacent cells, Thorium Cells output in a diamond shape two cells deep.
This extended area of coverage is a large change in the way the cell is used, as the heat connections no longer have to compete for space with Isolation. Whereas in all previous heaters, all four places where heat could be taken were also valid spots for isolation blocks, the extended area gives a grand total of twelve cells from which heat could be taken, only four of which are useable for isolation.
Without upgrades Thorium Cell will produce 150000000000*800=120000000000000 (120 T) heat in it`s lifetime. Assuming none of it gets wasted, the total profit is 48 T, once we subtract the hefty cost of 72 T.
It costs 50 Trillion Research Points to unlock. Researching Thorium Cells gives access to research Office 5, Underground Heat Pipes, Generator 4, and Protactonium Cells.