BTW, it's not "ground space" so much as the cubic capacity of the room - a 3x3 ground space with a 50 foot ceiling is obviously going to be able to handle that heat a lot better than the same area with a 4 foot ceiling.
Off the top of my head, I'd say that a minimum of 100 CF is needed (along with air-cooling the light).
Without air-cooling, the number of CF needed goes up bigtime.