Have you looked at the manufactures recommendations for the height? Every manufacture has there own recommendation of how far to hang the light I'd start there and if you're worried about heat burn.
I do have fans I’m not having a problem with the heat I just don’t know if I should run it because I don’t want to kill the seedlings from it being to bright.
use 23 watt cfl's for now but if the led light is about 3 feet away the seedlings should be fine. i use my 200watt home made led at that height and have only killed one seedling but that was because it got stuck in the jiffy pellet mesh.