It would depend entirely on how active the hour was. I find some of my classes are a constant sweat making hour and others not so full on, so i am sure in the heavy duty ( so to speak) classes the calories are turning to mush ... how many I have no idea.
One of my instructors did say she had been told a full on vigorous hour of BD can burn up to a 1000 cals. I think that is a bit much. But one never knows
~Mosaic