Well Im growing a Lowryder in my closet with a 600w HPS, and Ive had to take a shelf out to move the light up because of heat probs. It was at 2ft, but now its at 3ft, and the heat is fine as long as my window is open.
You also need to take into account that the plants will grow upwards (obviously), so theres nowhere near enough room there, unless you grow lowryders - and even then you might be hard pressed for space.