[pjc50]

5% of 1MW is obviously 20kW. That's rougly comparable to the "large" 68000BTU/hour space heaters.

On the other hand, it's well within the range of a conventional car engine cooling system: http://what-when-how.com/automobile/forced-circulation-water...

It depends somewhat on how hot the hot side can afford to get. The "weak link" will be getting the heat out of the cells themselves - it's no good if you can cool the exterior to 20C if the interior exceeds the safe limit of the cell.