The Overheater takes 200 water and 35 MJ (1 second for the recipe), to make 2400 steam @ 500C, which is about 240 MJ. Use the Rensuir turbines and the total output is close to 320 MW... for 200 water and < 40 MJ of chemical fuel/s (a packed wood briquette, 2 coal bricks).
It is very overpowered.
500C steam is 97 kJ / 1 unit. 200 steam at 500C would be 19.4 MJ, or, going the other way, 28 MJ (overheater @ 80% efficient) and 200 steam is 715 C (700 + 15). I think 200x 715 C steam makes more sense than changing the water-to-steam amount (although, 142.13 steam at 1000 C is 28 MJ, and is less fluid out than in).
I could also ask, why is the Overheater an assembler and not a boiler? Changing it now would break a lot of saves on prototype migration I think, but the OVerheater turns water to steam... sounds like a boiler.
Ironically, the science signs needed to make the Overheater can be gotten from making Rensuir turbines, so it costs almost nothing to actually make the Overheater itself. (making 24 rensuir turbines on the other hand takes a bit longer... the first time)
