We saw stoves/fireplaces like this in a bunch of taverns in Slovenia. Huge hulking tiled cubes around the center of the building that just radiated a pleasant heat from every square inch of the surface. I imagine it was quite efficient, with just a very low fire burning to keep it in equilibrium.

If it was a rocket stove, it was a very small very hot fire. I've had a bit of a love affair with rocket stoves lately (even replaced my BBQ/grill with one).